At least 40 people were killed in twin bombings in the Syrian capital of Damascus and airstrikes in the northwestern city Idlib on Wednesday, the sixth anniversary of the Syrian civil war.

In rebel-controlled Idlib province, airstrikes killed at least nine people, including children, according to the Britain-based Syrian Observatory for Human Rights. The pair of bombings in Damascus, one at the main courthouse and another outside a restaurant, killed at least 31 people and injured 130, according to state media.

The attacks came as the main Syrian rebel delegation boycotted Russian-led ceasefire talks in Kazakhstan aimed at ending the conflict that has claimed more than 320,000 lives.

“The attack came as a retaliation against the latest victories of the Syrian army and the political victories in Geneva and Astana,” a Syrian senior state legal official told state media, referring to this week’s talks in Astana, Kazakhstan and the parallel process in Geneva, Switzerland.

Just more than a year has passed since U.N.-brokered Syria talks led by Russia and the U.S. stalled in Geneva. Now, the current Russian-led process is hitting the same wall, as Turkey-backed rebels and Russia disagree about the future of President Bashar al-Assad in Syria.

Rebel spokesman Osama Abu Zaid said Monday the delegation would not attend the third round of Syria talks scheduled for Tuesday and Wednesday. The decision was “a result of Russia continuing its crimes in Syria against civilians and its support of the crimes of the Syrian regime,” he said, referring to what the rebels say are ongoing violations by Russia, the Syrian army and Iranian-backed militias of the current ceasefire in Syria. Russia and Turkey brokered the arrangement with the help of Iran last December after Russian airstrikes helped Assad defeat rebels in East Aleppo.

Russia dismissed the claims while the Syrian government envoy blasted the rebels’ decision from Astana, holding their main backer, Turkey, responsible.

“When one of the three guarantors breaks their commitment — and I mean Turkey — this means that Turkey must be the one that is asked about the non-attendance or participation of these armed groups,” Bashar al Jaafari, the Syrian government envoy, said Tuesday from Astana.

On Wednesday, al Jaafari said he was concluding his participation in the talks, following two days without the rebels. The rebel delegation denied reports from the Kazakh foreign minister that indicated they would attend the talks.

Bulent Aliriza, director of the Turkey Project at the Center for Strategic and International Studies, said Turkey’s contradictory policy in Syria — which backs rebels and calls for the removal of Assad from power while mending relations with Russia, Assad’s greatest ally — has been largely unsuccessful for the rebels.

“You have to think about how difficult it would be for the Turkish government to convince the opposition to sit across the table from people who are carrying out these attacks against them,” Aliriza said, referring to the breakdown in talks. “Turkey could not save East Aleppo from falling,” he added.

After Turkey’s President Recep Tayyip Erdogan met with Russia’s President Vladimir Putin to discuss Syria and trade in Moscow last week, Putin said the ceasefire in Syria was generally being observed and added Russia has “cautious optimism” that “a fully-fledged political resolution” could be reached. Erdogan added his assurance of Turkish military cooperation with Russia in the region.

Complicating Syria’s already complex battlefield alliances is the recent deployment of approximately 400 U.S. troops to northern Syria to support a U.S.-backed group of Syrian Arabs and Syria’s Kurdish YPG militia in the upcoming fight for the ISIS de facto capital of Raqqa in northern Syria. And on Wednesday, U.S. officials are saying the number of U.S. troops in Syria could go up by 1,000, according to the Washington Post. The U.S.-Kurdish partnership has rankled Washington’s relationship with the Turkish government, which considers the Kurds terrorists and has accused the U.S. of using one terrorist organization to fight another.

Gen. Joseph Votel, commander of U.S. Central Command, told the Senate Armed Services Committee last week that U.S. troops are currently in Syria’s northern city of Manbij in an effort to keep Kurdish and Turkish-backed forces from fighting and “keep people focused on the mission at hand, which is defeating ISIS.” Manbij is also occupied by Russian troops. Senate Armed Services Chairman Sen. John McCain (R-Ariz), who is wary fighting may break out in northern Syria among anti-ISIS groups converging there, replied “unless something changes, I foresee a train wreck here.”

“I’m not sure that the administration recognizes how seriously, particularly, President Erdogan views the threat that the Kurds pose,” McCain said.

Recent pictures of Russian troops wearing YPG badges on their uniforms in northern Syria have also unsettled Ankara.

As Kurdish fighters become increasingly vital in pushing ISIS from northern Syria, Aliriza, noting these recent shifts in Syria, said the perceived alliance of Russian troops with Kurdish fighters “has the potential to sour the relationship like the issue of YPG did with the U.S.”