More senators have joined the call for sending weapons to Ukraine, with Senate Armed Services Committee members John McCain (R-Ariz.) and Joe Donnelly (D-Ind.) writing a letter to President Barack Obama on Thursday to urge additional aid in the war against Russian-backed separatists.

“With Russia increasing its military presence on the Ukrainian border, by some estimates to as many as 40,000 troops and heavy weapons, there is growing concern that Russia could soon invade. Indeed, the Secretary General of NATO has said he believes there is now ‘high probability’ of such an invasion,” the letter reads. “In the face of this disturbing escalation in the conflict, we appreciate your leadership in mustering another round of strong international sanctions against Russia and in sending tens of millions of dollars in non-lethal military assistance to Kiev, including much-needed night-vision goggles, body armor and first aid kits, and other military equipment.

Sen. John McCain (R-Ariz.)
Sen. John McCain (R-Ariz.)

However, the senators note, “Kiev has identified critical needs to help them counter rebel capabilities gained through the flow of Russian support to the separatists. President Putin, undeterred by international condemnation, has provided heavy weapons to separatists, including tracked and armored vehicles and the advanced missile and radar systems that took down (a Malaysia Airlines passenger plane last month). In light of these developments, we should supply the Ukrainian military with appropriate defensive weapons such as anti-tank weapons to help them reclaim their territory.”

The SASC members also asked for increase intelligence-sharing to help Ukraine counter the separatists.

The letter comes just days after another senior SASC member, Bill Nelson (D-Fla.), told reporters before leaving for a trip to Ukraine, Lithuania and Turkey that he hoped the president would provide lethal aid as well, Defense Daily reported (Aug. 11, 2014).

Nelson said he was thankful the president had approved humanitarian aid, but “the place that I differ from the president is that he thus far has not been willing to give arms, or in other words lethal aid. I support giving arms to the government of Ukraine in order to help them protect themselves from the big Russian bear.”

“It is my belief you want to help them arm themselves,” Nelson said, advocating sending trucks, armored personnel vehicles, ammunition and weapons as needed.