WASHINGTON (AFP) - The United States on Sunday helped evacuate American, Canadian and other foreign citizens from Burundi, rocked by weeks of deadly street protests and an attempted coup, a State Department spokesman said.

Burundi's streets have been mired in violence since the announcement by President Pierre Nkurunziza that he would stand for a third term in office.

On Wednesday, a group of top generals tried to overthrow him while he was on a visit to neighbouring Tanzania, and Nkurunziza made his first public appearance since the attempted coup on Sunday.

The United States warned of the "volatile" situation in the landlocked, east African nation, and said it had assisted more than two dozen people to leave on planes that departed to neighbouring Rwanda.

"In addition to approximately 20 US citizens on the three commercial charter flights that went out on May 17 to Kigali, the US helped four Canadian citizens as well as other foreign citizens," Jeff Rathke said in a statement.

Rathke said the United States had received the requests for assistance from "several diplomatic missions. It said all US nationals that requested evacuation were able to leave Burundi, and that Washington routinely provides such assistance to foreign citizens on a "space-available basis."

It warned that the security situation remains unpredictable in Burundi, where weeks of protests have already left at least 20 people dead.

"The security situation remains fluid and volatile because of militia, military and security forces activity in Bujumbura," Rathke said. "There may be increased political tensions and civil disturbances related to these actions."