US troops swooped in on helicopters to evacuate embassy staff from Sudan's battle-torn capital, President Joe Biden announced Sunday, as other nations sought to help their citizens escape deadly fighting between rival generals.

France on Sunday also launched evacuation operations from the northeast African nation, where fighting has entered its second week.

Ferocious battles between the Sudanese army and a paramilitary group -- which has seen fighter jets launch airstrikes and street fighting with tanks in densely populated Khartoum -- have killed more than 400 people and left thousands wounded.

Biden, who said the US military "conducted an operation" to extract US government personnel, called for an immediate ceasefire and condemned the deadly violence.

"It's unconscionable and it must stop," he said in a statement.

Just over 100 US special operations troops took part in the rescue to extract fewer than 100 people, which saw three Chinook helicopters fly from Djibouti, staying on the ground in Khartoum for less than an hour.

France's foreign ministry said Sunday a "rapid evacuation operation" had begun, and that European citizens and those from "allied partner countries" would also be assisted, without giving further details.