One policeman has been killed and about 100 more injured outside Ukraine's parliament, after MPs gave initial backing to reforms for more autonomy in the rebel-held east, officials say.

National guardsmen were pelted with fire crackers and petrol bombs and an explosion was heard in the crowd.

MPs had just voted in a rowdy session to approve more powers in areas of Donetsk and Luhansk under control of pro-Russian rebels.

A fragile ceasefire is in place.

Pushing through greater autonomy for the rebel-held areas is a key part of the Minsk deal, originally signed in February.

During the summer fighting between Ukrainian army forces and the rebels has escalated. But the two sides agreed last week to halt the violence on 1 September, the day children in the region return to school.

Although the number of ceasefire violations appears to have fallen in recent days, a senior official in the OSCE international monitoring mission in Ukraine, Alexander Hug, warned that neither side was respecting the truce.

"Violations have become the norm," he told Swiss media.

Loud explosion

Shortly after 265 MPs backed the first reading of the decentralisation bill in the Ukrainian parliament, the Rada, the protests outside parliament became more intense.

A missile was hurled from the crowd of demonstrators, many of whom were carrying banners supporting ultra-nationalist Svoboda (Freedom) party.

A loud explosion rang out and an AFP reporter described seeing several people covered in blood.

One policeman's leg was torn off below the knee, Interfax Ukraine reported.

Journalists who had been covering the developments were also among the wounded.

Interior Minister Arsen Avakov said some 30 people had been detained and more would follow. He bitterly criticised Svoboda leader Oleh Tyahnybok, writing on Facebook that several explosive devices had been thrown by people wearing Svoboda T-shirts.

Almost 7,000 people have died since the conflict in eastern Ukraine broke out in March 2014, after Russia's annexation of the Ukrainian peninsula of Crimea.

Under the draft constitutional changes going through parliament, there will be a special law covering local government in rebel-held areas. However, parliament speaker Volodymyr Hroysman was adamant that would not mean special status for Donetsk and Luhansk, which rebel leaders have declared republics.

If President Petro Poroshenko is to succeed in pushing through the reforms, he will need the support of 300 of the Rada's 450 MPs, seen as a tall order for the Ukrainian leader.