ADDIS ABABA (Reuters) - The African Union said on Friday it was preparing to send 5,000 peacekeepers to Burundi to protect civilians caught up in a growing crisis, for the first time using powers to deploy troops to a member country against its will.

Burundi dismissed the announcement, saying no foreign force would get in without permission. But its neighbours have grown increasingly alarmed about the violence in the central African state which the United Nations says is on the brink of civil war.

Tensions have been running particularly high since gunmen attacked military sites in the capital Bujumbura last week, unnerving a region where memories of the 1994 genocide in neighbouring Rwanda are still raw.

The African Union’s Peace and Security Council said in a statement it had drawn up plans for the force, to be called MAPROBU, and had asked the U.N. Security Council to give it the final clearance it needed to get boots on the ground.

The U.N. Security Council has already been looking at ways to tackle the crisis, including sending peacekeepers.

“(The AU body) decides that MAPROBU shall have an initial strength of up to 5,000 military personnel and police,” including also human rights observers and military experts, it added.

A diplomat told Reuters late on Thursday the resolution marked the first time the AU had decided to invoke its charter’s Article 4, that gives it the right to intervene in a member state “in respect of grave circumstances, namely: war crimes, genocide and crimes against humanity”.

In Washington, the State Department said the United States was ready to support the African Union in its efforts to prevent further violence and achieve a political resolution to Brurundi’s crisis.

It said in a statement the United States had extended targeted sanctions against people whose actions “threaten the peace, security, and stability of Burundi” to four new individuals, bringing the total to eight. It did not give their names.

AT LEAST 400 KILLED

Burundi’s government spokesman, Philippe Nzobonariba, said the force would not be allowed in without permission. “They can’t invade a country if the latter is not informed and allow it,” he said on state radio.

“It would be better if they go to those camps in Rwanda where troublemakers train,” Nzobonariba added. The government has accused Rwanda of supporting rebels who are recruiting Burundian refugees, a charge Rwanda denies.

The United Nations says at least 400 people have been killed since April when President Pierre Nkurunziza’s decision to seek a third term in office triggered protests and a failed coup.

Rights groups have reported violent clashes between protesters and authorities, gun attacks and detentions of government critics. The government dismisses reports of rights abuses.

Hundreds of thousands have also fled the worst violence to hit the country since it emerged from an ethnically charged civil war in 2005.

Demonstrators said the president’s decision to stand in an election he eventually won broke constitutional term limits, while his supporters pointed to a court ruling allowing his bid.

Much of the latest violence appears to be along political divides. But diplomats fear a prolonged conflict could reopen old ethnic rifts.

The civil war pitted the army, which was at the time led by minority Tutsis, against rebel groups of the Hutu majority, including one led by Nkurunziza, an ethnic split mirrored in Rwanda.

The U.N. High Commissioner for Human Rights accused Burundi’s authorities on Thursday of dragging the country towards full-blown civil war and called for travel bans and asset freezes targeting key officials to try to halt the bloodshed.

Burundi’s presidency said the same day it was open to “broad-based inclusive dialogue”, though opponents have dismissed similar pledges in the past.

Other African leaders are also pushing to extend their terms beyond constitutional limits, despite criticism by the United States and other Western donors.

Rwandans voted on Friday in a referendum on changing the constitution that would allow President Paul Kagame to extend his term in office, possibly until 2034.