Speaking Sunday at the Munich Security Conference in Germany, U.S. Sen. John McCain criticized Russian President Vladimir Putin's intervention in Syria's nearly five-year civil war.
"Mr. Putin is not interested in being our partner," said McCain, chairman of the U.S. Senate's Armed Services Committee, adding that the Russian president wanted to "shore up the Assad regime."
Since intervening in the Syrian conflict in September, Russia has pursued a devastating air campaign from Hmeymim air base in Syria's Latakia province
, which has helped swing momentum in favor of Syrian President Bashar al-Assad.
McCain continued: "He wants to re-establish Russia as a major power in the Middle East. He wants to use Syria as a live-fire exercise for Russia's modernizing military, he wants to turn Latakia province into a military outpost from which to harden and enforce a Russian sphere of influence -- a new Kaliningrad, or Crimea -- and he wants to exacerbate the refugee crisis and use it as a weapon to divide the trans-Atlantic alliance and undermine the European project."
Russia annexed Crimea
, where it has a critical warm-water naval base in Sevastopol, from Ukraine in 2014, and gained possession of the seaport of Kaliningrad, a Russian exclave on the Baltic Sea, from Germany at the end of World War II.
Syrian opposition: 58 massacres of Syrian civilians by Russia
The comments came amid increasing criticism of Russia's actions in Syria, in the wake of a ceasefire agreed to by world powers Friday
, the details of which are still being worked out.
Western powers and Syrian opposition groups say Russia is bombing civilians and undermining any prospects for peace -- accusations that Russia denies.
Riad Hijab, former Syrian prime minister and head of the main Syrian opposition group, the High Negotiations Committee, said in Munich on Sunday that there had been "58 clear massacres committed by the Russian military against Syrian civilians alone in the last 10 days."
He later reiterated: "The action that I see is that Russia is killing Syrian civilians."
U.S. Secretary of State John Kerry said in Munich on Saturday
that Russia's strikes in Syria had been largely "against legitimate opposition groups."
And McCain continued the criticism Sunday, saying that the recent agreement on a cessation of hostilities would require "opposition groups to stop fighting, but ... allows Russia to continue bombing terrorists which it insists is everyone, even civilians."
"Russia has indiscriminately bombed civilians and moderate opposition groups for months with impunity," he said.
Obama, Putin speak
The conversation was "frank and constructive," the statement from the Kremlin said, adding it had been Obama's initiative.
Both parties gave a positive assessment of the call for a cessation in hostilities and agreed to step up cooperation through diplomatic channels and other agencies in order to see it implemented.
Putin also reiterated the need to establish a "common counter-terrorist front," with close contacts between U.S. and Russian defense officials "which would make it possible to combat ISIS and other terrorist organizations in more effective and better-planned fashion."
The White House said in a statement that the call was made to discuss the recent agreement and "stress the importance of rapidly implementing humanitarian access to besieged areas of Syria and initiating a nationwide cessation of hostilities."
In particular, it said, Obama underlined the importance of Russia "ceasing its air campaign against moderate opposition forces in Syria."
The two leaders also spoke about the situation in Ukraine, both sides acknowledged.
Syria writes to Security Council over Turkish shelling
The phone call came a day after U.S. Vice President Joe Biden spoke to Turkish Prime Minister Ahmet Davutoglu, urging Ankara to show restraint by ceasing artillery strikes on Kurdish forces in northern Syria. France also called on Sunday for Turkey to halt the bombardment.
Turkish forces shelled Kurdish units in the town of Azaz in northern Aleppo governate on Saturday and Sunday, killing two fighters from the U.S.-backed Democratic Syria Force and wounding seven others, according to the London-based monitoring group the Syrian Observatory for Human Rights.
The Syrian government condemned Turkey's actions Sunday and sent letters to the U.N. Security Council calling on it to intervene, according to Syrian state news agency SANA.
The White House said in a statement Sunday that Biden had pointed out to Davutoglu U.S. efforts to discourage Syrian Kurdish forces from exploiting current circumstances to seize additional territory near the Turkish border, and urged Turkey to show reciprocal restraint.
U.S. State Department spokesman John Kirby said in a statement Saturday that Turkey and the Kurdish forces shared a serious threat from ISIS just to the east of Azaz.
"We continue to encourage all parties to focus on this common threat, which has not subsided, and to work towards a cessation of hostilities, as agreed in Munich," he said.
Meantime, Turkish Defense Minister Ismet Yilmaz said that his country had "no intention to send Turkish soldiers to Syria," according to semi-official Anadolu news agency.
Anadolu reported that Yilmaz made the comments in a statement Sunday.