Clashes erupted outside parliament in Kiev on Monday as lawmakers gave initial approval to consitutional changes granting more autonomy to pro-Russian separatists in eastern Ukraine.

A blast was also heard outside parliament, an AFP correspondent said, although the cause was not immediately known.

About a dozen people were reportedly injured, an AFP journalist said.

Several people were seen bleeding, including police officers and apparently journalists, and lying on the ground in front of the parliament, the journalist said.

The Western-backed constitutional reforms are required under the terms of a  Western-backed peace deal signed in February, which called for Kiev to implement "decentralisation" by the end of this year.

But critics have branded the reforms "un-Ukrainian".

A total of 265 lawmakers voted in favour of the reforms at a stormy session of parliament in Kiev, with protests both inside and outside the buidling.

Dozens of demonstrators scuffled with police, AFP journalists saw. Protesters fired at least one smoke grenade that sent up a cloud of black smoke outside the building.

Tear gas was used by both sides, an AFP correspondent said.