Ukraine's president promised Wednesday to introduce a bill as early as next week that would offer greater autonomy to rebellious regions in the pro-Russia east, where separatists have been battling government troops for almost five months.

But President Petro Poroshenko said the regions would remain part of Ukraine and rejected the idea of federalization, something both Russia and the Russian-backed separatists are still pushing for even after a cease-fire that began Friday.

The cease-fire agreement, reached in Belarus, "envisages the restoration and preservation of Ukrainian sovereignty over the entire territory of Donbas, including the part that is temporarily under control of the rebels," Poroshenko said during a televised Cabinet meeting. "Ukraine has made no concessions with regards to its territorial integrity."

Ukraine and the West have repeatedly accused Russia of fueling the separatists with arms, expertise and even its own troops, something Russia denies. In late August, NATO estimated that more than 1,000 Russian troops were operating on Ukrainian soil, helping to turn the tide of the war in the rebels' favor.

Poroshenko has struggled to paint the Minsk cease-fire agreement — reached as the rebels waged a major counteroffensive that pushed back the Ukrainian troops who had encircled them — as a victory rather than a defeat. Poroshenko says since the agreement, 70 percent of the Russian troops in Ukraine had been withdrawn.

He also said 700 Ukrainian prisoners had been freed from rebel captivity and expressed hope that another 500 would be freed by the end of the week.

It was unclear, however, how many of those freed were soldiers rather than civilians. Col. Andriy Lysenko, spokesman for the Ukrainian National Security and Defense Council, told journalists Wednesday that only 20 servicemen had returned home so far. In Donetsk, a rebel spokesman said a planned exchange of 36 soldiers from each side had been put off until Thursday, blaming the government for the delay.

The president admitted that "implementing the cease-fire is very difficult" and accused separatists of "provoking" the Ukrainian troops.

The cease-fire has been violated numerous times. Ukraine says five servicemen have been killed and 33 injured since Friday. A volley of rocket fire could be heard in Donetsk late Tuesday, although the city council didn't report any casualties overnight.

Poroshenko was vague on the specifics of his bill. But a previous peace plan laid out in June envisaged protection for the Russian language, joint patrols of federal and local police and letting local representatives give their approval for governors, who are appointed by the central government in Kiev.

All of those concessions are minor in comparison to what the separatists want. At various times, they have demanded full independence from Kiev or union with Russia, something that Russian President Vladimir Putin has ignored. But even their concessions to having Ukraine become federalized would require local control over security forces and elections for governors.

Poroshenko may have difficulty crafting a bill that is palatable to both the separatists and his parliament, which is gearing up for a parliamentary election on October 26. The Ukrainian public has been largely supportive of the war in the east against the separatists.