A 400-strong Sudanese force arrived in Yemen's port city Aden Monday in support of pro-government forces preparing to confront a possible new offensive by rebels on the country's south.Yemen's loyalist forces, backed by Saudi-led coalition strikes, supplies and troops, pushed the rebels out of Aden as part of an operation launched in July to take back southern territories lost to renegade forces.Four other southern provinces -- Lahj, Daleh, Abyan and Shabwa -- were also retaken by the forces loyal to President Abedrabbo Mansour Hadi.But the Iran-backed rebels this weekend retook several positions in the south."More than 400 Sudanese soldiers landed in Aden" as part of the coalition battling the rebels since March, said a commander of Yemeni forces loyal to Hadi.These will join 500 Sudanese soldiers who arrived in Aden on October 19, part of whom were deployed in the main southern city and the strategic Al-Anad airbase in adjacent Lahj province, the source told AFP.Their arrival comes amid a mobilisation of loyalist forces to block a possible attempt by the rebels to re-enter Aden."General mobilisation was been declared in Daleh," where the rebels recaptured the province's second-city, Damt, on Saturday, a local official told AFP.A similar call was made in the coastal city of Dhubab, near the Bab al-Mandab strait, where the rebels achieved a "limited advance" during the weekend, a military source said.The rebels seized a military base in Dhubab on Saturday following deadly clashes with pro-government troops, according to military sources.Pro-government troops seized Dhubab early last month, giving them effective control of Bab al-Mandab, through which much of the world's maritime traffic passes.The rebels overran the Yemeni capital Sanaa last year and then advanced south to Aden, forcing Hadi and his government to flee to Saudi Arabia.Ministers from Hadi's government returned to Aden in mid-September after six months in exile in the neighbouring oil-rich kingdom.The United Nations says that around 5,000 people have been killed in Yemen's conflict since it escalated in March.