Republicans on the House Armed Services Committee sent an open letter to President Obama on Wednesday urging him to share new intelligence of Russian troop movements with the Ukrainian government.
The congressmen said they are "gravely concerned about the aggressive posture of Russian forces along the eastern border of Ukraine."
"There is deep apprehension that Moscow may invade eastern and southern Ukraine, pressing west to Transdniestria, and also seek land grabs in the Baltics," the letter reads, citing both classified and unclassified reports.
The letter also urges Secretary of Defense Chuck Hagel to "increase and enhance the alert posture and readiness of U.S. military forces in the region, and pursue additional measures to bolster the security of our eastern and central European allies and partners."
A separate letter containing classified intelligence was also sent to the White House on Wednesday.
"Russia's war on Ukraine has already started. It is time to stop speculating about possibility, and start dealing with reality," read a statement from Rep. Buck McKeon, R-Calif., chairman of the House Armed Services Committee.
Reps. Mac Thornberry, R-Texas, Randy Forbes, R-Va., Joe Wilson, R-S.C., Michael Turner, R-Ohio, Mike Rogers, R-Ala., Rob Wittman, R-Va., and Joe Heck, R-Nev., signed the letter along with McKeon.