Anti-government rebels in South Sudan attacked the key town of Bor on Tuesday, ignoring a deadline set by regional powers to stop fighting and hold peace talks.

Government troops were fighting forces loyal to former vice-president Riek Machar and a pro-Machar tribal militia known as the White Army, military spokesman Colonel Philip Aguer said on Tuesday.

Fighting started before dawn and involved tanks, rockets and small arms, said United Nations spokesman Joe Contreras in Juba, the capital. He said the airstrip in Bor was closed and it was unclear who was in control of the town.