Pentagon concerned about Russian troop build-up near Ukraine

The Defense Department’s top spokesman on Tuesday raised fresh concerns over a renewed build up of Russian troops along the border with Ukraine.

NATO leaders estimate around 20,000 Russian troops have amassed along the border with Ukraine. The Russian presence includes tanks, artillery and air defense systems, the leaders said in a statement.

On Monday, Russia's defense ministry announced that around 100 fighter jets, helicopters and bombers would conduct military exercises near the border later this week, a move that could worsen already frayed ties between Washington and Moscow.

While those forces are roughly equal to the amount Russia had on the ground in the spring, they are closer to the border and “are doing nothing but continuing to escalate the tension that exists inside eastern Ukraine,” Rear Adm. John Kirby said during a press briefing.

He declined to say whether the U.S. thought the forces could presage an invasion of Ukraine, but said the forces appear to be “very capable and very ready” for such action.

He also accused the Kremlin of providing lethal weapons to separatists in the eastern part of the country.

“We do continue to see the flow of some heavy equipment across the border to assist the separatists. Some of it’s ephemeral. It doesn’t stay. Some of it does,” Kirby told reporters. “It’s difficult to get a bead on exactly what’s going on and when but the support to the separatists continues and it needs to stop."

Kirby also said that around a dozen military personnel had landed in Kiev to help with the investigation to help investigate the downing of Malaysian Airlines Flight MH17.

The U.S. believes the airplane was brought down by pro-Russian separatists last month, a charge both Moscow and the rebels deny.

The team will not participate in actual recovery operations and would not leave the capital city, according to Kirby.

Instead they will “provide some advice and recommendations through the embassy staff to partner nations that  … are trying to either investigate or recover loved ones from that crash,” he said.