The United States is drawing up fresh sanctions against Russia for its role in fuelling the crisis in Ukraine, top US diplomat John Kerry warned Tuesday.

"We are in the process of preparing additional sanctions, with Europe," Kerry told reporters, shortly after the EU finally adopted broad economic measures against Moscow.

But he added that Russian President Vladimir Putin "still has a choice going forward with respect to his ability to be able to have an impact with the separatists."

Speaking after meeting with new Ukrainian Foreign Minister Pavlo Klimkin at the State Department, Kerry revealed he had again raised US concerns over Russia's role in stirring unrest in eastern Ukraine during a telephone call Tuesday with his Russian counterpart Sergei Lavrov.

The two men had "agreed that there is a way to try to put some very specific proposals on the table to try to move forward," Kerry maintained.

"But the Russians and their so-called volunteers are continuing to ship arms and funds and personnel across the border. We see this. There is clear evidence of it."

Over the weekend, US officials released what they say are images of Russian artillery firing from inside their country on Ukrainian military positions.

"President Putin can make a huge difference here if he chooses to, and we and our European partners will take additional measures and impose wider sanctions on key sections of the Russian economy if that is what we must do," Kerry said.

"We hope that it will not be necessary. And if Russia continues to go down this path, however, Russia will leave the international community with no choice."

The US secretary of state again slammed the difficulties being faced by international investigators trying to gain access to the site where a Malaysian airliner was downed 10 days ago, killing all 298 people on board.

"Without this access, they have no way to collect debris, no way to collect other evidence from the scene in order to be able to provide the kind of examination that is necessary," Kerry said.

"They still can't even ensure that all of the victims' remains have been removed, and that is an unsupportable burden for any family to have to bear, and it is an unacceptable standard for behavior.

"The site has to be cordoned off, the evidence has to be preserved, and Russia needs to use its considerable influence among the separatists in order to be able to help ensure this basic approach of common decency."