Burundi has moved closer to civil war after insurgents attacked military camps last week and authorities responded with house searches, arrests and alleged summary executions, the U.N. human rights chief said on Tuesday.

The fighting in the capital Bujumbura last week killed almost 90 people, the worst clashes since a military coup was foiled in May.

It follows months of sporadic violence and assassinations, mostly in the capital, between supporters and opponents of President Pierre Nkurunziza.

U.N. human rights office spokeswoman Cecile Pouilly told a news briefing that in November alone, U.N. monitors had recorded 56 incidents of extrajudicial killings and 452 cases of arbitrary arrests and detentions, while 389 arbitrary detained people were released.

The crisis in Burundi alarms Western powers, who worry it may slide back into conflict after emerging from an ethnically fuelled civil war 10 years ago. They fear it could destabilise a region where memories of the 1994 genocide in neighbouring Rwanda are still raw.

“With this latest series of bloody events, the country seems to have taken a new step towards outright civil war and tensions are now at bursting point in Bujumbura,” U.N. High Commissioner for Human Rights Zeid Ra’ad Al Hussein said in a statement.

After Friday’s fighting, security forces launched “intensive house searches” in Bujumbura’s Musaga and Nyakabiga districts, he said. Both areas saw protests earlier in the crisis against Nkurunziza’s re-election for a third term.

During the searches, the security forces “arrested hundreds of young men, allegedly summarily executing a number of them and taking many others to unknown locations,” Zeid said.

He urged “all actors in the current crisis, including political leaders and state authorities at the highest level, to take every step possible to stop this deadly escalation and engage in a meaningful and inclusive dialogue.”

There was no immediate response from the government, but it regularly dismisses accusations of rights abuses.

The government also says it is open to dialogue. Opponents say the government’s offer of talks has been a smokescreen because it has failed to allow discussion of core issues, such as the president’s current five-year term in office.

Opponents say the president violated a peace deal that ended the civil war by seeking a third term. Officials point to a ruling by the constitutional court that said he could run again.