WASHINGTON--U.S. intelligence officials presented their most detailed case yet Tuesday that Russian-backed Ukrainian separatists shot down a Malaysia Airlines jetliner last week, countering what American officials see as Russian efforts to muddy the waters with claims of Ukrainian culpability.

U.S. intelligence officials presented both photographic and circumstantial evidence to back their view that a likely SA-11 antiaircraft weapon fired from separatist-controlled territory shot down the commercial airliner, killing 298 people on board.

There is a "solid case it was an SA-11 fired from Eastern Ukraine under conditions created by Russia," a top U.S. intelligence official said.

Among evidence presented Tuesday: The U.S. detected a surface-to-air missile launch at the time that the airliner was hit, in roughly the same separatist-controlled area in Eastern Ukraine; there has been a growing flow of weapons from Russia to separatists over the last month; Russians have provided training for separatist fighters in southwest Russia on antiaircraft weapons and other arms; and separatists have downed more than a dozen aircraft during the conflict.

Russian President Vladimir Putin is making a "full court press" to spread a Russian version of events that try to pin the shoot-down on the Ukrainians, which is "not plausible to us," once senior intelligence official said.

A key goal of Tuesday's presentation was "not letting a Russian narrative get out there," said one senior U.S. intelligence official.

Russia has continued its support of the separatists since the crash of Flight 17, sending tanks and rocket launchers, U.S. intelligence officials said. "We don't think they have stopped," said one. "We think they continue to do it."

Officials acknowledged there are details of the missile launch and airline crash that the U.S. hasn't confirmed. For instance, they don't know who fired the SA-11--their names, ranks or nationality. They also don't know precisely why the missile was fired, but they said they believe it was mistakenly fired at a commercial aircraft.

Write to Siobhan Gorman at siobhan.gorman@wsj.com

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