European Union leaders were expected to decide Wednesday whether to toughen sanctions against Russia because of what they consider its destabilization of neighboring Ukraine.

Many of the 28 EU leaders coming into Brussels for an evening summit agree that Russia is still failing to take sufficient measures to help ease the crisis in eastern Ukraine, where separatists in two regions want to break away.

British Prime Minister David Cameron accused Moscow of continuing not to respect Ukraine's territorial integrity, and called that "unacceptable."

"We need to send a very clear message with clear actions at this (European) Council meeting tonight," Cameron said.

EU diplomats were looking at new sanctions that would go beyond the current travel bans and assets freezes against individuals but still fall short of full economic and trade sanctions.

An early draft of proposed new EU sanctions included an end to funding by the European Investment Bank and European Bank for Reconstruction and Development of new public sector projects in Russia, and suspension of many EU bilateral and regional cooperation programs with Russia.

But hours before the start of the summit Wednesday evening, the process was still in flux, with EU officials saying the language was still being worked on.

The United States is considering imposing unilateral sanctions on Russia for its actions regarding Ukraine.

At their last summit, on June 27, the EU leaders threatened to impose new measures if their demands on Russia and the pro-Russian fighters in eastern Ukraine were not met.

Germany said Ukraine says heavy weapons are still flowing to separatists across the Russian border, and there are increasing attacks on Ukrainian forces from Russian territory.

"Unfortunately not much has happened regarding the implementation of our expectations," German Chancellor Angela Merkel said in Brussels. "No hostages have been released, the border has not been secured, the contact group isn't working."

"That's why we will talk about new sanctions here because we believe that the Russian contribution to peace in Ukraine is not yet sufficient," Merkel said.