WILMINGTON, Delaware (Reuters) - United States Vice-President Joe Biden spoke to Ukraine President Petro Poroshenko on Thursday and offered US assistance to help determine what happened to a crashed Malaysian plane on the Ukraine border, the White House said.

Russian President Vladimir Putin offered condolences to Malaysia's Prime Minister over a Malaysian airliner that came down over Ukraine, Malaysia's Bernama state news agency reported on Friday. "The president of Russia asked the prime minister of Malaysia to convey his deepest sympathy and support to the victims' families," the news agency reported, citing Putin's official website.

The flight that crashed in eastern Ukraine on Thursday carried at least four French nationals on board, France's foreign minister said on Thursday.

Asked about reports there were four French nationals aboard the crashed flight, Foreign Minister Laurent Fabius said: "That's the minimum."

"An inquiry needs to be launched extremely quickly into what is an absolute major tragedy," Mr Fabius added, speaking on French BFM-TV during a trip to the Ivory Coast with President Francois Hollande.

Pro-Russian separatists in eastern Ukraine say they have found the "black box" flight recorder of the Malaysian airliner that crashed, killing 295 people, the Interfax news agency reported.

The information could not immediately be confirmed by Reuters.