Turkish President Recip Tayyip Erdogan was meeting with Russian President Vladimir Putin in Moscow Thursday for talks aimed at ending fighting in northwestern Syria. Both leaders agreed to a ceasefire scheduled to start at midnight after six hours of talks.

But if history is any judge, the agreement won't last long. Two previous ceasefire agreements failed spectacularly as Russia and their Syrian allies gained more territory that was held by Turkish-backed rebels. Moscow and Damascus claimed the operations were to combat terrorism.

If there is ever going to be a cessation of violence, it will likely have to be Turkey drawing a hard line, believes U.S. Ambassador James Jeffrey, U.S. Special Representative for Syria Engagement.

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"The Russians have turned down all of our offers for compromise and they are pressing for a military victory," Jeffrey told CBS News on Thursday.

"What the Turks are saying now and we support them 100% is there cannot be such ceasefires anymore. They have to be real. They have to be enduring. There has to be a line on the ground that nobody violates."

Syria's Idlib province in the northwest is the last stronghold of the Syrian rebels. Fighting escalated there in recent weeks, displacing nearly a million people. The situation has created what the United Nations calls a "grave humanitarian crisis."

Jeffrey says it goes beyond that.

"This is a humanitarian catastrophe but it's far more than this. It's a dangerous geostrategic escalation. It's a dangerous international situation that needs to be brought under control with a ceasefire," he said.

A Syrian government victory in Idlib may seem inevitable. Their army is still on the offensive. They continue to squeeze the province with air and artillery strikes.

But while Syrian President Bashar Assad succeeded in the past in purging rebel-held enclaves with the help of the Russians, Jeffrey said Idlib will be different.

"I do not think the Russians and Assad will win in Idlib and the reason is the Turks cannot back down or they will have 3 million new refugees on top of the almost 4 million that they have now from Syria and they cannot physically handle it," he said. "That's what we saw at the border (with Syria) and I do not think that there's any way possible for them to cope with that. So therefore, they're going to have to use their considerable military force to bring this offensive to a halt."

Turkey, the second largest member of NATO, launched Operation Spring Shield this week after at least 34 troops were killed in an airstrike in Idlib. In response to the strike, the Turkish military bombarded Syrian government positions that they claimed destroyed hundreds of vehicles and killed hundreds of regime troops.

During his talks with Erdogan, Putin expressed his regret about the killing of the Turkish troops, saying the Syrian army had not known their location.

Jeffrey, however, said it may not have been the Syrian army.

"We believe quite possibly Turkish elements having been bombed by Russian aircraft," he said.

He said the confrontation between Turkey and Russia creates a dangerous escalation in the region. "We have essentially a NATO country confronting at least Russian advisory teams, Russian surrogates, including the Syrian military, Hezbollah and certain Iranian Revolutionary Guard elements on the ground in Idlib today."

Jeffrey insists the United States is content to let Turkey take the lead in the war in Syria. But don't call this leading from behind, he said, but rather "being smart."

"Our first instinct is to support and help those or willing to fight themselves in this case that is the Turks," he said.

Part of that is the U.S. looking into ways to assist Turkey militarily, which could include Patriot surface-to-air missile batteries. But supplying Patriot missiles is controversial after Turkey purchased the advanced Russian S-400 missile defense system last year.

"We have one particularly problematic, outstanding issue that both the administration and the Congress is very concerned about, that's the Turkish purchase of the S-400," he said. "The main problem with the S-400 is it makes incompatible the use of the U.S. F-35 fifth generation stealth fighter."

Turkey purchased more than 100 F-35 warplanes, but U.S. lawmakers punished Turkey by barring the delivery of the planes.

That created tensions between Washington and Ankara. Perceived closeness between Putin and Erdogan in recent years has also led to tension.

Jeffrey downplayed any rift between the U.S. and Turkey.

"President Erdogan and President Trump have a very good relationship," Jeffrey said.

"This has been extremely expensive for Turkey, extremely expensive for the United States and we are trying to work our way through the problems that have emerged from the S-400."