Russia’s ambassador to the United Nations on Tuesday accused Ukrainian intelligence services of aiding rebels fighting Syrian President Bashar al-Assad’s government, saying some fighters were “openly flaunting” the association.

Rebels fighting with Islamist group Hayat Tahrir al-Sham (HTS) “have not only not concealed the fact that they are supported by Ukraine, but they are also openly flaunting this,” Vassily Nebenzia told the Security Council.

The envoy said there was an “identifiable trail” showing Ukraine’s GUR military intelligence service was “providing weapons to fighters” in northwest Syria.

“Ukrainian military instructors from the GUR are present… training HTS fighters for combat operations,” including against Russian troops in Syria, Nebenzia alleged.

A renewed offensive in the past week, led by HTS and its allies, has seen a massive shift in the long-frozen frontlines of Syria’s civil war, with the Islamist-led rebels advancing on Syria’s fourth-largest city Hama after capturing Aleppo.

Russia is one of Assad’s key allies. Its 2015 intervention in the Syrian civil war turned the tide in his government’s favor.

Amid the new offensive, a statement from Syria’s army command said its forces were striking “terrorist organizations” in north Hama and Idlib provinces, with Russian air support.

Ukraine’s foreign ministry said Monday that Russia and Iran — both supporters of Assad’s hardline rule — “bear the main responsibility” for the recent escalation in fighting.

Kyiv hit out at Assad for recognizing Moscow’s annexation of the Crimean peninsula in 2014, and said Ukrainians were also being targeted on a nightly basis by Iranian-designed drones.

“The Russian dictator (Vladimir) Putin and his allies in Iran continue to make every effort not to lose control over the puppet Syrian regime, which is associated by the majority of Syrians with inhuman cruelty, tyranny and crimes,” the ministry said.