Ukraine was on Tuesday reeling after fierce clashes in Kiev killed two policemen and wounded 140 people outside parliament as tensions flared over controversial legislation giving more autonomy to the rebels.

It was the worst unrest in the Ukrainian capital since a bloody uprising ousted former president Viktor Yanukovych in early 2014, unleashing the ­rebel insurgency in the ­industrial east.

The clashes erupted on ­Monday when hundreds ­gathered outside the ­parliament to protest after legislators gave ­initial backing to a bill ­granting a degree of autonomy to the rebels in eastern Ukraine.

The government blamed ultra-nationalists for the unrest, saying they detonated a live grenade near the entrance to the parliament building.

The chaotic scenes with swirling black smoke and baseball bat-wielding protesters carried echoes of the worst clashes of the Maidan uprising that ousted Yanukovych early last year.

"We have already found the perpetrators," pro-Western President Petro Poroshenko said in a televised interview on Tuesday. "The organizers, who were distributing baseball bats, who helped bring weapons, will also be found."

Poroshenko, who was to visit the wounded later Tuesday, branded the violence a "stab in the back" saying the perpetrators deserved "severe" punishment.

A member of the National Guard died on the operating table Monday, killed when a grenade fragment reached his heart. On Tuesday, a second member of the National Guard succumbed to injuries caused by shrapnel from the grenade, Interior Minister Arsen Avakov wrote on Twitter.

More than 140 people were being treated in hospital, officials said.

"According to our latest data, 141 injured people remain in hospitals all over Kiev," police spokeswoman Oksana Blyshchyk said.

She said 131 of the wounded were policemen and 10 of them were in a serious condition.

Poroshenko aide Olga Bogomolets said the most severely wounded suffered injuries to the stomach, lungs and brain.

Authorities pointed the finger at activists from the ultra-nationalist Svoboda (Freedom) party, but they denied responsibility.