Ukraine's highest court on Friday allowed parliament to vote on Western-backed constitutional amendments aimed at stemming daily bloodshed by giving pro-Russian insurgents partial autonomy in the separatist east.

The idea of granting at least three years of self-rule to rebellious parts of Ukraine's industrial war zone has struck a note of disquiet among many lawmakers and much of the Kiev media.

But it was inscribed in a truce deal that Ukrainian President Petro Poroshenko and Russia's Vladimir Putin signed off on in February in the Belarussian capital Minsk.

Parliament voted by an overwhelming majority on July 16 to ask Ukraine's constitutional court to rule whether such changes to the basic law were legal.

The former Soviet country's justice Vasyl Brintsev concluded without reservations that it was.

The idea of militia-run regions holding their own elections and setting up separate police forces "does not break or limit the rights and freedoms of (Ukrainian) people and citizens," Brintsev said in the decision.

Ukrainian President Petro Poroshenko leaves after his address in Kiev on July 1, 2015 Sergei Supinsky, AFP/File

The draft constitutional clause is part of a broader "decentralisation" proposal that should see Kiev cede some of its powers to all regions -- and assign especially broad ones to pro-Russian lands -- in the years to come.

One top Ukrainian deputy said a second of three votes on the changes should take place by the end of next month. Parliament would then need to muster a two-thirds majority in a final reading for the amendments to take effect.

Poroshenko called Friday's court ruling "an important step that moves us closer to momentous changes for the state."

"For the first time in Ukraine's history, its head of state and government are ceding a large degree of their powers to the regions," he wrote on his Facebook page.

"This will make our country powerful and whole."

- Buffer zone -

Both Washington and its EU allies believe that autonomy could satisfy separatist fighters and remove any arguments Russia may have for arming and funding their campaign -- support Moscow firmly denies ever giving.

But the suggested changes have been denounced as insufficient by the rebels and are unlikely to make an immediate impact on the ground.

Four civilians and three Ukrainian soldiers have been reported killed since Thursday in shelling attacks on disputed towns that straddle a frontline splitting the self-declared "people's republics" of Lugansk and Donetsk from the rest of Ukraine.

Ukrainian servicemen use an automatic grenade launcher during fights with the pro-Russian separatists near Avdeevka, Donetsk region, on June 18, 2015 Aleksey Chernyshev, AFP/File

The entire separatist region -- about the size of Wales -- accounted for just 2.6 percent of Ukraine's population but 15 percent of its industrial production before the war broke out with Kiev's new pro-Western government in April 2014.

Poroshenko's critics question whether Ukraine will ever be able to rebuild its imploding economy with the east's powerful coal mines and steel mills still under the insurgents' control.

But Kiev's Western governments are pushing for a resolution that could help start mending their relations with Russia and building stability across European Union's unsettled eastern edge.

The Minsk accord also demands the "withdrawal of all foreign armed formations" and Kiev's reestablishment of full control of Ukraine's border with Russia by the end of the year.

Poroshenko depends on foreign support in his standoff with Russia and has been defending the Minsk agreements against its fiercest domestic critics.

He hopes to strike a new demilitarisation agreement with the insurgents on Monday that requires both sides to pull back smaller-scale weapons from what should become a 30-kilometre-wide (18-mile-wide) buffer zone.

US State Department spokesman Mark Toner said "we strongly support President Poroshenko's call to sign an agreement on the withdrawal of heavy weapons under 100 millimetres in calibre."

"We urge all sides to implement such an agreement immediately," he told reporters on Thursday.