KIEV, Ukraine — A former Ukrainian president warned on Wednesday that the country is now on “the brink of civil war,” and Russia added to the gloom by announcing the suspension of its financial aid package, which was all that had been keeping Ukraine solvent.

Leonid M. Kravchuk, Ukraine’s president from 1991 to 1994, issued his warning while offering his services to Parliament in mediating negotiations between the government and opposition leaders on overhauling the Constitution to weaken the power of President Viktor F. Yanukovych.

But Parliament halted work for the evening without voting on the constitutional change or another measure to assuage tension.

President Vladimir V. Putin of Russia had told European Union leaders at a summit meeting Tuesday in Brussels that his government intended to fulfill its financial aid commitments to Ukraine in spite of negotiations here that could put a pro-Western government in power. Mr. Putin said the $15 billion aid package was for the Ukrainian “people.”