WASHINGTON — Before leaving on its recess, the Senate confirmed John F. Tefft as the United States’ ambassador to Russia, filling a post that had been vacant since February, when a frayed relationship between the two countries began to sink further over the separatist uprising in Ukraine.
Tefft, a career diplomat who had been the US ambassador to Ukraine, Georgia, and Lithuania, will arrive in Moscow as the Obama administration struggles to confront the Kremlin and fighting in eastern Ukraine worsens and grows in complexity after the downing of a passenger jet.
The administration faces “some of the most challenging times in the relations between the United States and Russia since the end of the Cold War,” Tefft said in July during testimony to the Senate Foreign Relations Committee.
President Obama told President Vladimir Putin of Russia on Friday that the United States remains deeply concerned that Russia is stepping up support for pro-Russian separatists in Ukraine, the Associated Press reported.
Obama later conceded that pressure from recently imposed US and European sanctions ‘‘hasn’t resolved the problem yet.’’
In a phone call between the two leaders, Obama also raised concerns that Russia violated a key Cold War era nuclear weapons treaty, the White House said.
The Obama administration has said Russia violated a 1987 treaty that bans all US and Russian missiles of intermediate range, meaning those that can travel between about 300 miles and about 3,400 miles.
Putin, in the call, characterized the sanctions as counterproductive, adding that they seriously damage bilateral cooperation and general global stability, according to a Kremlin report.
The previous US ambassador to Russia, Michael A. McFaul, resigned his post in February, ending a sometimes stormy two-year tenure that began with accusations by the Russian media that he was sent to help stir up widespread protests against Putin at the end of 2011.