MEGAN THOMPSON, PBS NEWSHOUR WEEKEND ANCHOR: Rebel-held areas around Aleppo, Syria, continue to be subject to fierce fighting, as government forces try to retake the city. And a new report from the independent Syrian Center for Policy Research estimates 470,000 Syrians have died in the war, almost double previous estimates.

"New York Times" reporter David Sanger is covering the conference, and he joins me now from Munich.

David, a day after the cease-fire plan was announced, confidence in it doesn't seem to be very high, correct?

DAVID SANGER, THE NEW YORK TIMES: It certainly doesn't.

We heard Sergey Lavrov, the foreign minister of Russia, say today that he thought maybe 49 percent. And somewhat sarcastically we heard Secretary of State Kerry later on, "Oh, he's that optimistic?" I think Mr. Kerry has got a higher sense of probability that this will work.

But there's an awful lot, Megan, that can get in the way of this. There are two parts to this.

The first part is humanitarian deliveries to the besieged cities in Syria. I think there's a fair bit of optimism that those will be stark, and the question is how long will they last?

The second and much harder part of this is what most people would call a cease-fire and what they are calling for these purposes "a cessation of hostilities". Even Secretary Kerry has said this may only be a pause. The idea is give enough of a quiet moment to actually get negotiations going.

MEGAN THOMPSON: It seems that as talk of this cease-fire have increased, so have tensions between the U.S. and Russia. Is this just posturing, or is it part of something bigger?

DAVID SANGER: You know, it really is something bigger. Think of the different elements. We have the continued tensions and sanctions over Ukraine. We have the increased Russian patrols off of the British coast, off of most of Europe, more nuclear forces being exercised.

And I think here, the Americans were taken a little bit by surprise at the speed at which the Russians ended up entering that air war over Aleppo, and thus gaining some leverage that the U.S. right now does not have in return.

MEGAN THOMPSON: One of the issues that has caused tension between the two countries is this issue of military coordination in Syria. Can you talk a little bit about that and if there's been any movement on that front?

DAVID SANGER: The United States has been very, very cautious about getting into coordination with the Russians because they say, look, the Russians are deceiving people about who they're striking.

They're striking many of the rebel groups aligned with the United States other ands who have been opposing Assad, and saying that they're just striking the two terror groups that have been designated by the United Nations, the Islamic State, and the al-Nusra Front.

But the coordination is going to be unavoidable over the next few weeks because they're supposed to work together in a joint task force headed by Mr. Kerry and Mr. Lavrov, to pick out targeting.

They're supposed to work together on the cease-fire, and they're supposed to work together on the humanitarian aid. I don't know how you do that without something that approaches coordination, made all the harder by the fact that the United States is, of course, back into the sanctions business against the Russians right now.

MEGAN THOMPSON: David, you can talk a little bit about the timetable, how this will all work on the ground?

DAVID SANGER: Well, Megan, the way it's supposed to work is that the humanitarian relief is supposed to begin within days, and Secretary Kerry said today that the trucks are loaded up and ready to go. But that's a different thing than actually getting them into where they're supposed to be. And the Russians are supposed to be airdropping some aid. Some of the big questions is, where they aired drop it and to which people?

If a week from today, we still see a lot of fighting going on, then you'll know that this wasn't working the way it was supposed to.

MEGAN THOMPSON: All right. David Sanger of "The New York Times" — thank you so much for joining us.

DAVID SANGER: Thank you, Megan. Good to be back with you.