U.S. Vice President Joe Biden told Ukrainian President Petro Poroshenko on Tuesday that Washington and the European Union are preparing further sanctions against Russia, even as a rocket attack in the eastern Ukrainian city of Donetsk killed 11 people.

The announcement comes ahead of a meeting between EU leaders to discuss plans such as freezing the Russia-based programs of the European Investment Bank and the European Bank of Reconstruction and Development, according to Agence France-Presse, or AFP. The EU has so far avoided imposing economic sanctions against Moscow, despite approving asset freezes and travel bans on 60 Russian and pro-Russian Ukrainian persons, accused of destabilizing Ukraine.

“The leaders discussed Russia’s ongoing support for the separatists and apparent escalation of the conflict over the last few days," the White House said, in a statement, according to Reuters, adding: “The vice president told President Poroshenko that the United States was engaging with European leaders to discuss the imposition of costs on Russia for its continued escalation of the conflict."

White House spokesman Josh Earnest said Tuesday, according to AFP: "The longer that this goes on, the more difficult it will be for us to put Ukraine on the stable, sound footing, both politically and economically, that we would like to see them be on," while the White House also stressed that conditions laid down by the G7 for Russia to help Ukraine reduce violence in the region, have not been met.

At the EU meeting Wednesday, where issues such as the successor to Catherine Ashton as the EU's next foreign policy chief will be addressed, leaders are also expected to take a hard look at the future of the Ukraine crisis. A new round of sanctions against pro-Russian separatists and Moscow is "looking very possible," AFP reported, citing an EU official.

“This is neither phase 2 or phase 3 but something different," the EU official told AFP, adding that the consideration of new EU sanctions is not influenced by the U.S., but "some of the entities and persons that will be added (to the proposed sanctions) are already on the US sanctions list." The U.S. has reportedly been urging EU leaders to broaden financial sanctions and impose restrictions on the sale of arms to Russia.

Meanwhile, separatists blamed Ukrainian forces for a rocket attack Tuesday in the rebel-held town of Snizhne in Donetsk, while Kiev denied the attack without any further explanation, Associated Press reported. Dmitry Tymchuk, a military analyst who works closely with Ukraine's defense ministry, said that "only Russian aviation could have performed the airstrike on Snizhne," AP reported, citing his Facebook account.