Burundi's president, Pierre Nkurunziza, has declared that any African Union (AU) peacekeepers deployed to his country will be met with a fight from Burundian forces.

Nkurunziza's comments - his most confrontational yet - was in response to the AU's announcement that it would send 5,000 troops to protect civilians in the state amid a mounting political crisis, even without government consent.

The AU announced its planned action two weeks ago, invoking for the first time powers to intervene in a member state against its will.

"Everyone has to respect Burundi borders," Nkurunziza said on Wednesday in comments broadcast on state radio.

"In case they violate those principles, they will have attacked the country and every Burundian will stand up and fight against them ... The country will have been attacked and it will respond," he said, in his first public response to the AU plan.

Other government officials have already said any peacekeepers arriving without Burundi's permission would violate its sovereignty.

More than 220,000 people have fled and at least 400 killed since the crisis erupted in April, triggered by Nkurunziza's bid for a third term.

Opposition groups took to the streets saying he was violating constitutional term limits. But he pointed to a court order allowing his campaign and was re-elected in a disputed July vote.

A failed coup, continued clashes and gun attacks in the central African state have unsettled a region where memories of the 1994 genocide in neighbouring Rwanda are still raw.

The government claimed there is no threat of genocide, however a recent AU investigation reported arbitrary killings, torture and the arbitrary "closure of some civil society and the media".

Additional reporting by Reuters