WASHINGTON — President Barack Obama told Russian President Vladimir Putin Friday that the United States remains deeply concerned that Russia is ramping up support for pro-Russian separatists in Ukraine. It was the first conversation between the leaders since the U.S. and Europe slapped a new round of economic sanctions on Moscow.
In a phone call, 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 U.S. and Russian missiles of intermediate range, meaning those that can travel between about 300 miles and about 3,400 miles.
In Moscow, the Kremlin said Putin had characterized the sanctions during the phone call as counterproductive, adding that they seriously damage bilateral cooperation and general global stability.
The Kremlin said both Obama and Putin underscored the urgency for bringing an end to fighting in eastern Ukraine and spoke positively about a meeting that took place the day before in Minsk, Belarus, among members of a diplomatic ‘‘contact group’’ pursuing an end to hostilities. That group includes representatives from Russia, Ukraine and the Organization for Security and Cooperation in Europe.
In a lengthy statement, the Russian Foreign Ministry also criticized the U.S. report that included the allegation that Russia had violated the treaty.
‘‘The claims are put forward practically without evidence, based on strange deductions and suppositions,’’ the statement said.
The Obama-Putin call came as the U.S. was poised to send an additional $27 million in military aid to Ukraine in an effort to strengthen the struggling nation’s national guard and beef up its ability to protect its border. The money comes amid increased congressional pressure on the administration to increase support for Ukraine as it battles Russian-backed separatists.
U.S. officials said the aid includes $19 million for the Ukrainian National Guard and $8 million for border security, including surveillance equipment, armored vehicles, and small boats.
On Thursday, five Republican senators sent Obama a letter calling on Obama to supply Ukraine with weapons and not just non-lethal assistance.
‘‘A failure to provide appropriate lethal assistance to Ukraine would lead Putin to conclude that the West is not willing to stand against his aggression and clear violations of international law,’’ said the letter signed by Sens. Kelly Ayotte of New Hampshire, James Inhofe of Oklahoma, John McCain of Arizona, Marco Rubio of Florida and Lindsey Graham of South Carolina.
At least 12,000 Russian troops are gathered close to Ukraine’s eastern border. The U.S. has complained about Moscow sending heavy military equipment across the border to support the separatists, including surface-to-air missile systems that officials say were likely used to shoot down a Malaysian Airlines flight.
Also Friday, Vice President Joe Biden called Ukrainian President Petro Poroshenko to announce the border assistance and to discuss the ‘‘increasing prevalence’’ of artillery and rocket fire into Ukraine from Russia, the White House said.
According to the White House, Poroshenko did say that access to the site of last month’s Malaysian airline crash that killed nearly 300 people had been secured despite continued fighting in the vicinity. The crash, which the West has blamed on separatists using Russian-made missiles, is the subject of an international investigation.
Associated Press writers Lolita C. Baldor and Josh Lederman in Washington and Jim Heintz in Moscow contributed to this article.