WASHINGTON (CNN) -

Top American officials harshly criticized Russia on Friday for its continued support of pro-Russian rebels in Ukraine following the downing of a Malaysia Airlines jetliner.

President Barack Obama said Friday that Russian President Vladimir Putin has the "most control" over the situation in eastern Ukraine as intelligence indicates that rebels most likely shot down Flight 17 from an area they control with a surface-to-air missile.

Nearly 300 people were killed in Thursday's disaster, including one American.

Obama said the rebels' sophisticated weaponry and training needed to shoot down aircraft "is coming from Russia" and said the United States could ratchet up sanctions on Russia if it continues to support the rebels.

But he stopped short of blaming Russia or Putin for the debacle in eastern Ukraine.

But Senior Republican lawmakers, most outspoken on foreign affairs and often critical of Obama's foreign policy, didn't hold back.

They were quick and direct in blaming Putin and called for additional, more stringent sanctions against Russia.

"I think he is responsible," said Sen. John McCain, a member of the foreign affairs and homeland security committees. "I mean, it wasn't Vladimir Putin that pushed the button to launch the missile, but the whole scenario, including the buildup of Russian troops across the border ... I think that he gave them the material and wherewithal to do it -- or facilitated it."

Those calls come after Republicans have criticized Obama for months for not taking a harder line on Russia or meeting Ukrainian demands for more military assistance as it battled rebels.

But now McCain said he sees "no separation" between Putin and the Ukrainian rebels, calling that movement "clearly orchestrated" by Moscow.

And U.S. Ambassador to the United Nations Samantha Power said investigators can't rule out the possibility that Russia may have helped the separatists operate the complex missile system.

Power also emphasized the crucial role Russia has played in the conflict in Ukraine, as well as the role the country can play to bring peace to the region.

"Russia can end this war. Russia must end this war," she said.

Sen. Mark Kirk of Illinois said he believes operating the missile system "would need backup from a nation-state like Russia."

"That would mean that Russian armed forces are directly involved in this wrongful death of roughly 300 people," Kirk asserted.

Russian officials rebutted even the suggestion of Russian involvement and instead blamed Ukraine for creating a volatile environment in eastern Ukraine.

And while there are conflicting reports over whether the plane's flight data and cockpit voice recorders have been taken to Russia, Russian Foreign Minister Sergey Lavrov said Moscow would "insist on the most objective, most open and independent investigation" into the incident.

Still, Kirk called for the Justice Department to file a wrongful death lawsuit "against Russian assets in the U.S." and said the United States should target those assets to show Moscow that "tens of millions of dollars will be lost."

Rep. Peter King, a member of the House Homeland Security Committee, drew similar conclusions. He called Putin "largely responsible" for the downing of the passenger act, which Ukrainian officials have labeled as a terrorist act.

"If you're a world power and you give this type of sophisticated weaponry to insurrectionists, you're responsible for what happens after that," King said. "This violates to me all norms of international behavior by a world power."

U.S. officials have not yet concluded whether separatists obtained the missile system used to down the Malaysian airliner from Russia, though Obama confirmed that Russia has supplied heavy weaponry to the separatists.

King said Russia's arming of the rebels with sophisticated weaponry amounted to "almost criminal negligence," even though he does not believe Putin wanted the passenger plane to be downed.

And though the tragedy came a day after additional U.S. and European Union sanctions were leveled against Russia, McCain, King and other Republican lawmakers renewed calls for tougher sanctions.

As retribution, King said the United States should consider further action such as preventing the Russian airliner Aeroflot from landing at U.S. and other Western airports.

And King claimed such a ban would have a "devastating effect on the Russian economy."

King's comments came after Oklahoma Republican Rep. Tom Cole called for a "stronger response" during an interview with CNN because "pinprick sanctions aren't going to get the job done."

Cole also called for direct military assistance to Ukraine, which he said is "fighting for its survival." That's a request the Kiev government has voiced to officials in Washington, asking for armament and military advice.

"I think that's an unmistakable sign that we're going to support them, that we're going to try to give them the wherewithal to defend their territorial integrity."

Even before U.S. officials confirmed the plane was shot down by pro-Russian separatists, Sen. Lindsey Graham, a South Carolina Republican, said Russian or separatist involvement would be a "game-changer."

Graham said that kind of information should trigger tougher sanctions from the United States and more support from other countries.