By M. Bilal Kenasari with additional reporting from Michael Hernandez

WASHINGTON 

U.S. lawmakers are drafting legislation that would send arms to Ukraine if President Barack Obama will not do it, a prominent Republican senator said Thursday.

“The U.S. must act with urgency to provide defensive lethal assistance to Ukraine,” said Sen. John McCain, because Russia's continued aggression in the face of increased sanctions "is the gravest threat to European security in decades."

McCain led a bipartisan group of senators at a news conference to stress the importance of sending lethal arms to Ukraine.

"We must help Ukraine to defend itself against Russian aggression," said Democratic Sen. Jack Reed..

White House press secretary Josh Earnest said Obama is currently weighing the possibility of delivering lethal aid to Kiev, but "one of the concerns that we have about providing military assistance is it does contain the possibility of actually expanding bloodshed. And that's actually what we're trying to avoid."

Despite U.S. and European sanctions on Russia since Moscow invaded Ukrainian territory early last year, annexing the Crimean Peninsula, Russia has not relented and continues to arm, train, and back rebels in eastern Ukraine. 

German Chancellor Angela Merkel and French President Francois Hollande flew to Kiev Thursday with a fresh peace proposal to end ongoing bloodshed. 

"We certainly are encouraging and supportive of ongoing efforts to try to find a peaceful diplomatic resolution to the conflict in Ukraine," Earnest said. "One concern that we have, however, is that previous diplomatic efforts have resulted in agreements that the Russians and the separatists that they back in eastern Ukraine didn't live up to"

Merkel is expected to visit Washington on Monday. A "substantial part" of her discussions with Obama will focus on the situation in Ukraine, Earnest said.

Ukrainian President Petro Poroshenko said his country needs modern weapons to combat the pro-Russian separatists in eastern Ukraine who have modern weapons, allegedly provided by Russia.

According to the UN High Commissioner for Human Rights, more than 5,300 people have been killed and 12,200 others injured in eastern Ukraine since April 2014 during the ongoing conflict between the Ukrainian army and pro-Russian separatists.