KIEV, Ukraine (AP) — A grenade exploded outside Ukraine’s parliament during a nationalist protest against a vote to give greater powers to separatist regions in the east, killing one police officer and injuring more than 100, the interior ministry said.

The clashes marked the worst outburst of violence in the capital since the government took power in February 2014.

The decentralization of power was a condition of a truce signed in Minsk in February aimed at ending the fighting between Ukrainian government troops and Russia-backed separatists that has left more than 6,800 dead since April 2014. But some Ukrainians oppose changing the constitution, saying that it would threaten the country’s sovereignty and independence.

In a televised address, Ukrainian President Petro Poroshenko called the bill, which was adopted on Monday as “a difficult but a logical step toward peace,” and insisted that it wouldn’t give any autonomy to the rebels.

The officer who was killed in the clashes on Monday was a 25-year-old conscript, Interior Minister Arsen Avakov told reporters. He said that 122 people were hospitalized — most are officers, but the number also includes Ukrainian journalists and two French reporters.

No injuries were immediately reported among several hundred protesters including 100 die-hard activists, most of whom were members of Svoboda, a nationalist party that holds only a handful of seats in parliament. The protesters were carrying sticks and truncheons. Some of them were masked.

Avakov said that about 30 people have been detained, including the person who threw the grenade. Avakov identified the grenade thrower as a Svoboda member who fought in the east in one of the volunteer battalions which are loosely controlled by the government.

Poroshenko described the clashes outside the parliament as an attack on him and pledged to prosecute “all political leaders” who were behind the clashes.

“There’s no other way to describe what occurred outside the Rada other than a stab in the back,” he said of the clashes outside parliament.

Poroshenko said the vote confirmed Ukraine’s “position as a trusted partner which fulfills its international obligations” and the country would have risked losing the support of the West and being left “alone with the aggressor.”

A total of 265 deputies in the 450-seat parliament gave preliminary approval Monday to the changes proposed by President Poroshenko. Three parties that are part of the majority coalition in parliament, however, opposed the constitutional changes.

“This is not a road to peace and not a road to decentralization,” said the leader of one of those parties, former Prime Minister Yulia Tymoshenko. “This is the diametrically opposite process, which will lead to the loss of new territories.”

Parliamentary speaker Vladimir Groisman denied that the changes would lead to the loss of the Donetsk region, where there have been clashes with separatists.

With the decentralization bill, Poroshenko found himself in a tight spot. While Ukrainian nationalists fear that the bill would incite separatism, Russia-backed rebels in the east and Moscow say the bill doesn’t give regions enough powers and is short of the pledges Kiev made in Minsk.

Prime Minister Arseniy Yatsenyuk, in a live address on television, called for life imprisonment for the person who threw the grenade and said the right-wing protesters were “worse” than the separatist rebels because they are destroying the country from within “under the guise of patriotism.”

“The cynicism of this crime lies in the fact that while the Russian federation and its bandits are trying and failing to destroy the Ukrainian state on the eastern front, the so-called pro-Ukrainian political forces are trying to open another front in the country’s midst.”

He called on all Ukrainian political parties to rally around the government and condemn the violence.

A final vote on the constitutional changes will be held during parliament’s fall session, which begins on Tuesday. No specific date has yet been set.

Avakov blamed the clashes on the Svoboda party, which polled under 5 percent in last year’s parliamentary election, and its leader, Oleg Tyahnybok, who stood side by side with Avakov during the anti-government protests which toppled then-president Viktor Yanukovych in February 2014.

“No political differences can justify what you did outside the Rada today,” Avakov said, referring to the parliament.

Svoboda blamed the government, saying that it “provoked Ukrainians to protest” by presenting a bill which is tantamount to “capitulation to the Kremlin.”

Kremlin spokesman Dmitry Peskov, in comments to Russian news agencies, voiced Moscow’s concern about the clashes in Kiev, but wouldn’t comment on the bill.

In Berlin, German Chancellor Angela Merkel said she’s open to holding a new summit with the leaders of Russia, Ukraine and France on the settlement in eastern Ukraine.

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Yuras Karmanau reported from Minsk, Belarus. Nataliya Vasilyeva in Moscow and Geir Moulson in Berlin contributed to this report.

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A previous version of this story has been corrected to show that the age of the dead police officer is 25, not 24.