(Adds Biden comment, 7th paragraph, U.S. lawmaker comment, paragraphs 10-11)
By Jeff Mason
WILMINGTON, Del., July 17 (Reuters) - U.S. President Barack Obama and Russian President Vladimir Putin discussed a passenger plane that was brought down along the Russian-Ukrainian border on Thursday during a phone call prompted by a new round of U.S. economic sanctions against Moscow.
Obama went ahead with a day trip out of Washington as the Ukraine crisis flared anew, amid reports that 23 Americans were among the 295 people aboard the Malaysia Airlines plane that went down along the Russia-Ukraine border.
"Obviously, the world is watching reports of a downed passenger jet near the Russia-Ukraine border, and it looks like it may be a terrible tragedy. Right now we are working to determine whether there were American citizens on board," Obama said at the start of a speech about the U.S. economy in Wilmington, Delaware.
Before leaving the White House, Obama spoke by phone with Putin. On Wednesday, the United States imposed the most wide-ranging sanctions yet on Russia for its aggression in Ukraine.
Moscow had requested the call. As the two leaders spoke, the first reports of the crash emerged, and Putin brought them up at the end of the conversation, White House spokesman Josh Earnest said.
Earnest told reporters on Obama's Air Force One flight from Washington to Delaware that Obama was briefed on the crash and directed top U.S. officials to remain in close contact with Ukrainian officials.
Vice President Joe Biden said during a speech in Detroit that the jet was shot down, "not an accident, blown out of the sky."
Biden earlier spoke on the phone with Ukrainian President Petro Poroshenko, offering assistance to help determine what happened to the downed Boeing 777 and why, the White House said.
UNPREDICTABLE ELEMENT
The crash injected an unpredictable element into the increasingly violent confrontation between Ukraine and Russian-backed separatists in eastern Ukraine.
Republican lawmakers, who have called for tough U.S. action against Moscow over Ukraine, quickly called for retaliation against Russia if it were found to have been involved in the crash.
"I believe there should be serious consequences if we find out that it was either Russian agents, Russian equipment or Russians directly that was responsible for the downing of this airliner," New Hampshire Republican Senator Kelly Ayotte said in a speech in the U.S. Senate.
Obama, determined not to appear to be a hostage of world events, went ahead with his trip after warning Putin that the United States could impose more sanctions on Russia if Moscow does not take steps to de-escalate the Ukraine crisis.
He flew to Wilmington, where he ate a hamburger with a supporter and gave a speech about the need for more U.S. infrastructure spending, and planned to attend two Democratic fund-raising events in New York later.
The new round of U.S. sanctions included penalties against Russia's largest oil producer, Rosneft and other energy, financial and defense firms.
Obama told Putin "additional steps are on the table if Russia doesn't change course," Earnest said.
"The United States is committed to ensuring that this international norm of countries respecting the territorial integrity of other countries is prioritized."
"The president's made clear that the international community, the United States and our European allies are willing to take steps and impose economic costs on Russia if they decline to respect those basic norms," Earnest said. (Additional reporting by Steve Holland and Patricia Zengerle in Washington. Editing by Jonathan Oatis)
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