HARI SREENIVASAN: More American troops are heading for Syria as the U.S. looks to press the fight against ISIS. This comes just days after the secretary of defense announced the deployment of additional forces to Iraq to take on the militants there.

PRESIDENT BARACK OBAMA: I have approved the deployment of up to 250 additional U.S. personnel in Syria, including special forces, to keep up this momentum.

HARI SREENIVASAN: With that, President Obama pledged to boost the number of American troops inside Syria by five-fold. Most are special forces, and the president said again to PBS and CBS News host Charlie Rose they won't be in a combat role.

PRESIDENT BARACK OBAMA: Although we are not going to be sending ground troops in to fight, we are going to try to find out what works and then double down. And one of the things that's worked so far is us putting special forces in for training and advising of local forces, but also intelligence-gathering.

HARI SREENIVASAN: The first 50 special forces troops deployed to Syria last fall. They have helped opposition fighters make gains, and the Pentagon says one of the goals now is to capture Raqqa, the Islamic State's de facto capital.

PETER COOK, Pentagon Press Secretary: And we think this deployment will certainly help to amp the pressure even higher at a critical time and perhaps, again, speed up the overall timeline for when we might be able to retake — when these forces can retake Raqqa.

HARI SREENIVASAN: Turkey has also exchanged artillery fire with ISIS along its southern border. Meanwhile, the cease-fire in Syria's other war, between government forces and rebel groups, is unraveling. In recent days, fighting has erupted around contested Aleppo, the country's largest city.

Opposition groups say government airstrikes killed dozens of people there over the weekend.

MAN (through interpreter): Around five people died. I carried two dead, one woman from this location and a man from nearby. The attacks on Aleppo in this latest period have been fierce and strong.

HARI SREENIVASAN: The resumption in heavy fighting has all but derailed U.N. efforts at peace talks in Geneva. U.N. mediators met with Syrian government officials today, but the main opposition group backed out of the discussions last week.

For more on all this, I'm joined now by Andrew Tabler of the Washington Institute. He's in Moscow learning more about Russia's role in Syria. And Nancy Youssef, she is the senior national security correspondent for The Daily Beast.

Nancy, let me start with you.

What's the purpose of these additional troops? What are they going to be doing on the ground?

NANCY YOUSSEF, The Daily Beast: There are upwards of 250 special forces and support staff, medical staff and otherwise, and their job there is to build a capable, bigger, stronger Syrian democratic force that could potentially and eventually go in reclaim the city of Raqqa, Islamic State's capital in Syria.

Their mission is twofold, to work with Kurdish forces and provide them with support, and then to also find Arab forces who will work with the Kurds. Because Raqqa is an Arab city, U.S. military believe that Arab fighters should be in to reclaim the city and lead the fight to reclaim Raqqa.

HARI SREENIVASAN: Andrew, strategically, how likely is that to happen?

ANDREW TABLER, Washington Institute for Near East Policy: The Kurds are quite strong fighters. They lack depth, particularly demographic depth among the Arab populations in Raqqa.

That's why, as Nancy said, the Syrian democratic forces is a way to get those Arab forces to work together with the Kurds and hopefully oust, eventually, the Islamic State from Raqqa.

HARI SREENIVASAN: Nancy, is the Pentagon concerned about the increased military activity that's been happening from Russia right now just in the past few weeks?

NANCY YOUSSEF: Some people are and some people aren't.

They're having a hard time really assessing with certainty whether this is an attempt by the Russians to really escalate their presence in Syria or this is a rotational movement that's happening now, that they're not seeing what portends of a full-fledged assault. While they're seeing incremental increases by the Russians, they're also seeing the withdrawal of some of their assault aircraft.

And there has been a lot of sort of wait and see in terms of assessing the Russian movement in Syria and what it means. This all comes in the backdrop of a cessation of hostilities agreement that appears to be in peril. And so, because of that, it's been hard to make, from what I hear in the Pentagon, definitive assessments on what the Russians are doing in Syria right now.

HARI SREENIVASAN: Andrew Tabler, what's behind some of these moves where the Russians seem to be pulling some equipment back and putting other equipment in?

ANDREW TABLER: Well, there is a real concern about the negotiations that are going on in Geneva. They felt previously that President Assad perhaps received too much Russian support. He was becoming increasingly rigid in his negotiating positions.

They were a little bit disappointed with him on the battlefield as well. He only gained about 5 percent back of Syrian territory over the last few months. But, in reality, someone among the opposition has shot down three regime planes in the last two months.

And I think that's the reason why we have seen some Russian aircraft cycled out of Syria and some helicopters with some countermeasures brought in that can make their forces more effective.

HARI SREENIVASAN: Nancy, is there concern in the Pentagon right now that this could draw out into something much longer? I mean, the phrase usually has been mission creep or resource creep.

NANCY YOUSSEF: Well, the military doesn't really embrace the idea of the term mission creep, but you are starting to hear the term resource creep, because the reality is this strategy against the Islamic State hasn't changed.

The goal is to degrade and ultimately defeat ISIS, as the president spelled out in September 2014. The resources keep changing towards that. And so there is some frustration in the Pentagon about the incrementalism of the deployment of troops.

And some are even openly asking what would have happened had, instead of sending 200 here and 200 there, 1,000 or 2,000 had been deployed earlier on? Would the war against the Islamic State being going quicker?

And so, today, you really started to hear the phrase resource creep about whether sending in troops incrementally is less for military reasons and more for political, and whether that calculation is actually delaying or slowing down the effort to defeat the Islamic State.

HARI SREENIVASAN: Andrew Tabler, also, the city of Aleppo right now, a large city in Syria, it seems to be almost poised for a significant onslaught.

ANDREW TABLER: That's right.

During the cessation of hostilities which is not a cease-fire, there has been a lot of fighting and a lot of raids, particularly by the regime, to close the ring around Aleppo. We think that they intend to close it and then squeeze, which will then expel people from the neighboring areas and also create a huge humanitarian disaster.

The question is, will the Russians go along with it or will they hold back as negotiations continue in Geneva? But since those negotiations aren't going well, we will have to wait and see what the Russians choose in the coming days.

HARI SREENIVASAN: Nancy, it seems the military has a couple of different lines of thinking here. On the one side, there's the Assad regime, and there's the ISIS attacks, right? So how do they deploy their military resources effectively enough?

NANCY YOUSSEF: What you're seeing is a real focus on the defeat of the Islamic State from a military perspective.

You will hear that said repeatedly. And the deployment of these forces both in Iraq and Syria sort of suggest that. In Iraq, you have had more forces moved along the route to Mosul, which is ISIS' capital in Iraq. And in Syria, these forces are going to be going in the northeast corner of Syria, where Kurdish forces have been able to move toward Raqqa.

And so militarily you're seeing a focus on the defeat of the Islamic State and not a focus on the Assad regime. That may be Russia's focus, but there has been a real effort by the Pentagon to keep the focus on the defeat of that terror group.

HARI SREENIVASAN: Andrew, when you talk about these — not just the peace talks that don't seem to be going well or the cessation that isn't going well, that tension between the United States and Russia right now on trying to go on these multiple fronts and trying to get cooperation from the Russians?

ANDREW TABLER: That's right.

It's strange. You know, in Syria, we're negotiating with Russia, and also trying — the Russians desperately want military cooperation in Syria as well, at the same time that planes are buzzing our battleships in the Baltic Sea.

HARI SREENIVASAN: All right, Andrew Tabler joining us from Moscow, Nancy Youssef of The Daily Beast, thanks so much.

NANCY YOUSSEF: Thank you.