Putin 'stalling' on MH17 response: Amb. Michael McFaul

Putin showing disregard for humanity: Expert

Though President Vladimir Putin has denied allegations of Russian complicity in the downing of Malaysia Airlines Flight MH17, mounting international pressure to take further action and assist the investigation will soon force him to quit "stalling," a former U.S. ambassador to Russia told CNBC on Monday.

"He's got to make a decision here whether he just doubles down and supports the rebels or whether he uses this tragedy as a moment to say, 'Enough is enough. We will negotiate. We will press for negations with these rebels,'" Michael McFaul, who served as U.S. ambassador to Russia from 2011 to 2014, said on "Squawk on the Street."

He spoke before President Barack Obama issued a statement outside the White House pressing Putin to be more cooperative.

Read MoreObama presses Putinon MH17 downing probe

Mikhail Klimentyev | AFP | Getty Images

Pro-Russian rebels in eastern Ukraine are suspected of shooting down the jetliner with a missile, killing 298 people. In the aftermath, Secretary of State John Kerry expressed disgust at the rebels' "grotesque" mishandling of the bodies.

Television images of the rebel-held crash sites, where the remains of victims had lain decomposing in fields among their personal belongings, have turned initial shock and sorrow after the disaster into anger.

"It is atrocious what is happening there. It is just awful," said McFaul, adding Putin should send Russian troops into eastern Ukraine to secure the crash site.

Read MoreCondemnation of Russia bad and likely to get worse

"He could be providing exactly that kind of assistance, and I think [the inaction] shows his disregard for humanity in a tragic way and it's deeply depressing to me," McFaul said.

McFaul said he thinks sanctions against Russia will force Putin to "change his behavior." However, "as long as Putin is in power, I think we're going to have this level of conflict in Russia."

Read MorePutin blames Malaysian plane tragedy on Ukraine

—By CNBC's Drew Sandholm, with Reuters.