DAMASCUS — The Kremlin vowed on Thursday to press on with its assault in Syria, while U.S. officials searched for a tougher response to Russia’s decision to ignore the peace process and seek military victory on behalf of President Bashar al-Assad.

Moscow and Damascus launched an assault to recapture the rebel-held sector of Aleppo this month, abandoning a new ceasefire a week after it took effect to embark on what could be the biggest battle of a nearly six-year war.

Rebel fighters have launched an advance of their own in countryside near the central city of Hama, where they said they made gains on Thursday.

The United States and European Union accuse Russia of torpedoing diplomacy to pursue military victory in Aleppo and say Moscow and Damascus are guilty of war crimes for targeting civilians, hospitals and aid workers to break the will of 250,000 people living under siege inside Syria’s largest city.

The Russia and the Syrian governments say they are targeting only militants.

Deputy Secretary of State Antony Blinken told lawmakers that President Obama had asked staff to look at how Washington might respond.

“The president has asked all of the agencies to put forward options, some familiar, some new, that we are very actively reviewing,” Blinken said. “When we are able to work through these in the days ahead we’ll have an opportunity to come back and talk about them in detail.”

Kremlin spokesman Dmitry Peskov said Russia would “continue the operation of its air force in support of the anti-terrorist activity of Syria’s armed forces.”

Peskov said Washington was to blame for the fighting, by failing to meet an obligation to separate “moderate” rebel fighters from those he called terrorists.

Russian Deputy Foreign Minister Sergei Ryabkov expressed outrage on Thursday at U.S. statements that he said amounts to support for terrorism

Ryabkov was referring to a statement made by State Department spokesman John Kirby who said on Wednesday that Russia had an interest in stopping the violence in Syria because extremists could exploit the vacuum there and launch attacks “against Russian interests, perhaps even Russian cities.”

“We cannot interpret this as anything else apart from the current U.S. administration’s de facto support for terrorism,” Ryabkov said.

“These thinly disguised invitations to use terrorism as a weapon against Russia show the political depths the current U.S. administration has stooped to in its approach to the Middle East and specifically to Syria.”