The United States said Monday that it had closed ranks with European allies to impose further sanctions on Russia if Moscow continues to destabilize eastern Ukraine.
"We are well aligned now on what a next round of economic sanctions would look like, in addition to continuing to look for individuals who one would sanction," Assistant Secretary for Europe Victoria Nuland told a think tank in Washington.
The US and the European Union "are now working on a series of sanctions in the energy sector, in the banking sector, in the defense sector," she said at the German Marshall Fund.
Nuland accused Russia of undertaking "further efforts to aid and abet separatists in this extremely dangerous way" by sending tanks and rocket launchers, a charge Moscow denies.
"There is no question that we had a serious deterioration on the ground over the last week," she said, pointing to the downing of a military plane by pro-Russian rebels that killed 49 Ukrainian troops.
Nuland though welcomed recent contact between newly elected Ukrainian President Petro Poroshenko and his Russian counterpart Vladimir Putin.
The US and Europe are evaluating the situation in Ukraine "on a daily basis" while sending a signal to Putin "that if he doesn't change course, there will be costs," she explained.
Nuland reiterated that Washington disapproves of the sale of French Mistral warships to Moscow.
"We made it clear well before the Ukraine crisis that we had large concerns about whether Mistral was the right thing to be sending," she said.
"We have not been shy about saying that the timing is certainly wrong," she added, stressing that the US "will continue to make this point."
France's 2011 agreement to sell the ships to Russia triggered protests from the United States and other NATO allies.
Paris has so far resisted pressure to suspend the controversial $1.2 billion contract.