WASHINGTON — With the peace process stalled and violence escalating in Ukraine, a bipartisan coalition in Congress is defying President Obama and European allies by pressing the administration to provide weapons to the embattled nation.

The Senate has included provisions in its military policy bill to arm Ukraine with antiarmor systems, mortars, grenade launchers and ammunition to aid in its fight against Russian-backed separatists. It would also prevent the administration from spending more than one half of $300 million in aid for Ukraine unless 20 percent is earmarked for offensive weapons. The House has passed a similar measure.

So far, the Obama administration has refused to provide lethal aid, fearing that it would only escalate the bloodshed and give President Vladimir V. Putin of Russia a pretext for further incursions.

The push by lawmakers to arm Ukraine’s beleaguered armed forces threatens to open a rift between the United States and key allies, especially Germany and France, at a time when the Obama administration has been working to demonstrate unified support for extending European economic sanctions against Russia that are scheduled to expire at the end of July.