Last Updated Jul 17, 2014 6:20 PM EDT
Vice President Biden said that Malaysia Airlines Flight 17 "apparently had been shot down" and "blown out of the sky" over eastern Ukraine Thursdayduring a flight from Amsterdam to Kuala Lumpur.
"We don't have all the detail yet," Biden said during a speech to Netroots Nation, a gathering of progressive activists in Detroit. But he said it appeared the plane was "shot down, not an accident, blown out of the sky."
As Biden was speaking, CBS News National Security Correspondent David Martin reports that U.S. military intelligence strongly believes that the plane was brought down by a surface-to-air missile as it flew at 33,000 feet over the war zone in eastern Ukraine.
Earlier Thursday, President Obama said that the crash "looks like it may be a terrible tragedy," and offered U.S. assistance in determining what happened.
"Right now we're working to determine whether there were American citizens on board. That is our first priority and I've directed my national security team to stay in close contact with the Ukrainian government," Mr. Obama said during a speech in Wilmington, Del. "The United States will offer any assistance we can to help determine what happened and why and as a country our thoughts and prayers are with all the families of the passengers wherever they call home."
Biden also said the U.S. was still working to determine whether there were any Americans on board.
"This is truly a grave situation. Nearly 300 souls have been lost. The families need consolation and our prayers and there are many question that need to be answered and we'll get those answers and we will take the next steps accordingly," he said. "It's important to get the bottom of this sooner or later because of the possible repercussions that could flow from this beyond the tragic loss of life."
The vice president also said he spoke by phone with Ukrainian President Petro Poroshenko and offered U.S. assistance from the National Transportation and Safety Board as well as other experts in the community.
The Ukrainian president accepted the assistance, Biden said, and the U.S. experts "will be on their way rapidly to see if we can get to the bottom of this."
Mr. Obama also spoke with Poroshenko as well as Prime Minister Najib Razak of Malaysia by phone.
Martin reports that if a missile shot the plane down, it would have had to be a Russian-made surface-to-air missile system, complete with radar, fire control, launcher and missile. A shoulder-fired missile could not have reached the altitude at which the plane was flying.
On two occasions earlier in the week, U.S. intelligence determined that surface to air missiles had shot down a Ukrainian cargo plane and a Ukrainian Frogfoot jet fighter. Both of them were flying above 20,000 feet, which is above the range of shoulder-fired missiles, Martin said.
Senate Intelligence Committee Chairwoman Dianne Feinstein, D-Calif., said after a briefing for her committee that the plane "appears" to have exploded in midair although U.S. intelligence to be able to determine exactly what happened in a day or so.
The system that detects ballistic missile launches did not detect the kind of launch that could have brought down an airliner, but it is not programmed to do so. There are other satellites and ground-based radars capable of detecting the kind of missile that could have brought down the plane.
The president discussed reports of the downed jet in a call with Russian President Vladimir Putin Thursday morning, although the White House did not provide any details about their conversation. The two leaders spoke after the U.S. moved to deepen sanctions against key sectors of the Russian economy in response to the continued violence by pro-Russian separatists in eastern Ukraine.
On Capitol Hill, the Senate Intelligence Committee was already set to receive a briefing on the Ukraine-Russia conflict. CBS News Congressional Correspondent Nancy Cordes reports the lawmakers will also be given a preliminary intelligence briefing on the downed jet.
Sen. John McCain, R-Ariz., has already begun speculating about the possibility that pro-Russian separatists were responsible for the crash and said Putin should "pay a heavy price," although he cautioned it was too soon to know exactly what happened.
"It's an outrageous and incredible act of terrorism that people [should] be held responsible and not only be people directly responsible, but indirectly," McCain said, according to Roll Call. "And if these are ... separatists, which are also Russian, Vladimir Putin should be paying a heavy price. But I am not concluding yet that until we find out all the information."
He also told reporters that there should be an American response "within minutes" if Russia is found to be responsible.
"We're gonna have to enact sanctions that mean something and we'll have to give arms to the Ukrainians which we have refused to do so far shamefully," if the Russians were responsible, he said.
House Speaker John Boehner, R-Ohio, called for reflection instead of a snap response to the crash.
"Many innocents were killed today. It is horrifying, and we await the facts. Right now, we should all take a moment to reflect, count our blessings, and convey our prayers to the loved ones of the victims," he said in a statement.