Later, Putin said Ukraine bears responsibility for the crash. But he didn't address the question of who might have shot down the plane and didn't accuse Ukraine of doing so.
"This tragedy would not have happened if there were peace on this land, if the military actions had not been renewed in southeast Ukraine," Putin said, according to a Kremlin statement issued early Friday. And, certainly, the state over whose territory this occurred bears responsibility for this awful tragedy."
Britain has asked for an emergency meeting of the U.N. Security Council on Ukraine.
The RIA-Novosti agency on Thursday quoted rebel leader Alexander Borodai as saying discussions were underway with Ukrainian authorities on calling a short truce for humanitarian reasons. He said international organizations would be allowed into the conflict-plagued region.
Aviation authorities in several countries, including the FAA in the United States, had issued warnings not to fly over parts of Ukraine prior to Thursday's crash, but many airliners had continued to use the route because "it is a shorter route, which means less fuel and therefore less money," said aviation expert Norman Shanks.
Within hours of Thursday's crash, several airlines, including Lufthansa, Delta and KLM, released statements saying they were avoiding parts of Ukrainian airspace.
Malaysia Airlines said Ukrainian aviation authorities told the company they had lost contact with Flight MH17 at 1415 GMT (10 a.m. EDT) about 30 kilometers (20 miles) from Tamak waypoint, which is 50 kilometers (30 miles) from the Russia-Ukraine border.
It said the plane was carrying 280 passengers and 15 crew members. It had left Amsterdam at 12:15 p.m. and was due to arrive at Kuala Lumpur International Airport at 6:10 a.m. Friday.
Anton Gerashenko, an adviser to Ukraine's interior minister, said on his Facebook page the plane was flying at an altitude of 10,000 meters (33,000 feet) when it was hit by a missile from a Buk launcher, which can fire up to an altitude of 22,000 meters (72,000 feet). He said only that his information was based on "intelligence."
Igor Sutyagin, a research fellow in Russian studies at the Royal United Services Institute, said both Ukrainian and Russian forces have SA-17 missile systems — also known as Buk ground-to-air launcher systems.
Rebels had bragged recently about having acquired Buk systems.
He said Russia had supplied separatist rebels with military hardware, but he had seen no evidence "of the transfer of that type of system from Russia." The weapons that the rebels are known to have do not have the capacity to reach beyond 4,500 meters. (14,750 feet)
A launcher similar to the Buk missile system was seen by Associated Press journalists earlier Thursday near the eastern Ukrainian town of Snizhne, which is held by the rebels.
The Malaysia Airlines plane was delivered to the company on July 30, 1997, according to Flightglobal's Ascend Online Fleets. It has more than 43,000 hours of flight time and 6,950 takeoffs and landings.
Poroshenko said his country's armed forces didn't shoot at any airborne targets.
"We do not exclude that this plane was shot down, and we stress that the Armed Forces of Ukraine did not take action against any airborne targets," he said. "We are sure that those who are guilty in this tragedy will be held responsible."
The Kremlin said Putin "informed the U.S. president of the report from air traffic controllers that the Malaysian plane had crashed on Ukrainian territory" without giving further details about their call. The White House confirmed the call.
Separatist leader Andrei Purgin told The Associated Press that he was certain that Ukrainian troops had shot the plane down, but gave no explanation or proof for his statement.
Purgin said he did not know whether rebel forces owned Buk missile launchers, but said even if they did, they had no fighters capable of operating it.
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