By Kristina Wong - 04/24/14 12:22 PM EDT
Pentagon officials are seeing Russian troop activity along Ukraine's eastern border, after the Russian defense minister announced new "exercises" there following a clash between Ukraine forces and pro-Russia insurgents.
"We have seen some movement associated with this announcement, but it's too soon to tell exactly what it is," said Army Col. Steve Warren said Thursday at the Pentagon.
"We have to react to these developments somehow," Shoigu said in a televised statement, according to The Associated Press.
Shoigu said the new exercises will involve ground troops in the south and west of Russia, and air forces patrolling the border, according to the AP.
U.S. officials say Russia has massed 40,000 troops along the south and eastern border of Ukraine. Shoigu told Defense Secretary Chuck Hagel last month they were there for exercises, but no exercises have taken place yet.
"The Russian announcement of additional exercises on the Ukrainian border is exactly opposite of what we've been calling on the Russians to do, which is deescalate the situation," said Warren.
"So we again call on them to act responsibly to de-escalate the situation and to help all parties bring this crisis to a peaceful resolution," he said.