A Ukrainian national guardsman was killed and nearly 90 others wounded by grenades hurled from a crowd of nationalist protesters on Monday as they were guarding parliament where lawmakers backed giving more autonomy to rebel-held areas.

The violence, which the government blamed on the main nationalist party, and division in the pro-Western camp in parliament suggested President Petro Poroshenko will struggle to push through key parts of a faltering peace agreement reached in February for eastern Ukraine.

Poroshenko sprang to the defence of the constitutional reforms following the clashes outside parliament, where deputies loyal to him managed to push through a first reading of a "decentralisation" draft law – but only in the face of strong criticism from some of his political allies.

In a message to the nation, he said that if parliament had not passed the draft, in line with Kiev's commitments at the peace talks in Minsk, Belarus, Ukraine would have been in danger of losing the support of its Western allies.

"There would have been a real possibility of us being left alone with the aggressor," he said.

The violence came after 265 deputies voted in favour of the bill, 39 more than that required to pass, at a boisterous session with many deputies shouting "Shame!" and rhythmically beating parliamentary benches.

Opponents of the bill, which supports a law giving certain self-management rights to separatists controlling parts of Donetsk and Luhansk regions, said it played into Russia's hands and would lead ultimately to Ukraine losing control in the east.

They objected to the separate legislation on local self-governance which they fear will give the separatists the right to form their own courts and militia and create a special relationship with Russia.

It would allow Russian to be the chosen language of people living in these regions and grant amnesty to separatists who had previously taken part in military action against Ukrainian forces.

Smoke bombs, then grenades

Elements in the crowd, many of whom carried banners from the nationalist Svoboda (Freedom) party, pelted black-helmeted national guardsmen with fire-crackers and smoke-bombs after the vote. Then, police said, grenades were thrown.

Interior Minister Arsen Avakov, blaming Svoboda in a tweet, said nearly 90 national guardsmen had been hurt, four of them with serious wounds to the eyes, stomach, neck and legs, by explosive devices lobbed from the crowd.

About 30 people were arrested, including a man suspected of throwing grenades, Avakov said.

Prime Minister Arseny Yatseniuk also blamed Svoboda, which has its main power-bases in western Ukraine, while Poroshenko said "pseudo-patriots" had been behind the violence.

The national guardsman killed was a 25-year-old who had been called up only in spring. Avakov said he had died from wounds caused by grenade splinters.

Though the bill passed on its first reading, many coalition allies, including former prime minister Yulia Tymoshenko, spoke against it. And, despite his firm words in support of it, it is far from certain that Poroshenko will be able to whip up the necessary 300 votes for it to get through a second and final reading later this year.

Approval of legislation for special status for parts of Donetsk and Luhansk regions, which are largely controlled by Russian-backed separatists, is a central element of the Minsk deal.

Though a ceasefire is under pressure from sporadic shelling and shooting which government troops and rebels blame on each other, Western governments see the deal as holding out the best possible prospects for peace and are urging Ukraine to abide by the agreement.

Border control

"We have to support the international 'anti-Putin' coalition," said Yuri Lutsenko of the Poroshenko bloc, referring to Russian President Vladimir Putin.

Poroshenko defended his strategy, saying that the main parts of the self-governance law would come into force only when local elections had been held in accordance with Ukrainian law, Russian forces had left Ukraine and after Ukraine had restored control over the border with Russia.

But opponents maintained it gave Putin the upper hand.

"This is a diametrically opposed process which forces us to lose territory," said Tymoshenko. "Putin does not need the Donbass (the name for the industrialised east). He needs war in Ukraine. Our task in the vote is to get back to negotiations on the right road to bring peace, not the illusion of peace."

The dissent in parliament and protests outside showed that Poroshenko will have an uphill task selling vital parts of the Minsk agreement to his people and increasingly restive pro-government paramilitary groups before the turn of the year.

That is when other elements of the agreement, including local elections, are supposed to be in place and Ukraine is supposed to have regained control of its border with Russia.

More than 6,500 people have been killed in the east since pro-Russian separatists rebelled against the Kiev government after Russia annexed Crimea in response to the ousting of a Moscow-backed president by street protests and his replacement by a pro-Western leadership.