As donors pledged more than $10 billion in aid to Syria on Thursday, the Russian government said it suspected that Turkey was planning a military invasion of the country. The allegation is the latest step in a deteriorating relationship between Moscow and Ankara since Turkey shot down a Russian plane in late November.

“We have serious grounds to suspect Turkey of intensive preparations for military intrusion into the territory of the sovereign state — the Syrian Arab Republic,” said Igor Konashenkov , a Russian Defense Ministry spokesman, according to state news agency Tass. “We are registering an increasing number of signs of the Turkish armed forces’ hidden preparations for active operations on the territory of Syria.”

If Turkey is planning an incursion it would mark a serious escalation in the Syrian war that began in 2011, which displaced millions and left more than 250,000 people dead. Turkey accused Russian airstrikes of causing approximately 70,000 people to flee the city of Aleppo as Syrian government forces continued to advance on the heavily-bombed city, Reuters reported. Aleppo is only 30 miles from Turkey’s border.

Turkish President Recep Tayyip Erdoğan accused Russian airstrikes of derailing the first peace talks held in two years about the war in Syria.

“Russia is continuing to kill people in Syria,” Erdoğan said, the Wall Street Journal reported. “Could there be such a peace gathering?”

Russia began airstrikes in Syria at the end of September that have aided the regime of Syrian President Bashar Assad and allowed the government to gain back ground held by rebel groups supported by Turkey. The Russian government confirmed Wednesday that one of its military advisors had been killed in Syria.

Speaking at the gathering of leaders pledging aid Thursday, U.N. Secretary General Ban Ki-moon said that bombings and aid blockades had undermined the peace talks.

“There is no military solution,” Ki-moon said. “Only political dialogue will rescue the Syrian people from their intolerable suffering.”