Nimule - A heavily-armed Ugandan military convoy crossed into South Sudan on Thursday to evacuate citizens trapped by recent fighting in the capital Juba, an AFP reporter at the border said.The convoy of around 50 trucks escorted by machine gun-mounted armoured vehicles crossed the border at Nimule to rescue Ugandans in the capital 200km to the north and open up a secure corridor for fleeing civilians who have been attacked by bandits and renegade soldiers."We plan to go to Juba to extract 3 000 Ugandans stranded by fighting, but that number may grow as we will evacuate anyone of any nationality who wants to leave," said army chief Brigadier Leopold Kyanda. "There may even be some South Sudanese who want to leave.""Juba is totally peaceful and calm now and we do not expect any problems. The problems could be on the road where there are a few thugs. The first responsibility of any UPDF soldier is to protect himself and we are confident in this," Kyanda said.Kyanda said the mission would likely last "two to three days".The Ugandan army joined the conflict in South Sudan soon after it began in December 2013, fighting on the side of President Salva Kiir against a rebel force led by Riek Machar, now the country's vice president.The Ugandan presence helped prevent the capital from falling into rebel hands while its attack helicopters were deployed to bomb rebel soldiers out of regional towns. Ugandan troops only pulled out late last year.Although military officials insist Thursday's incursion is a straightforward evacuation mission, an intelligence officer speaking on condition of anonymity said some Ugandan troops may remain in Juba."Why not? We have the capacity to support the government of South Sudan and we were there before," said the plain-clothed officer accompanying the convoy.