A battalion of 400 Sudanese soldiers arrived in the Yemeni port city of Aden on Monday, ready to be deployed against a possible new offensive by Houthi rebels in the south of the country.

The fresh deployment will join 500 other Sudanese soldiers who entered the country on 19 October to support the anti-Houthi fighters.

Sudan is part of a Saudi-led coalition that has been fighting to push back Houthi rebels who took over the capital in September 2014. Riyadh is seeking to reinstall exiled President Abd Rabbuh Mansour Hadi.

In August Sudanese officials announced that after they joined the coalition, Saudi Arabia deposited $1bn in the central bank. The reasons for the desposit were not disclosed.

Total casualty figures for the Sudanese troops already in the country are unknown, although an official with the Sudanese defence ministry acknowledged on 24 October, five days after they entered Yemen, that 22 of their troops had been either killed, injured or kidnapped.

It remains unclear where exactly the new troops will be sent, but forces loyal to exiled President Hadi are now mobilising in Dhaleh province, some two hours north of Aden, after Houthi fighters recaptured Dhaleh province’s second town over the weekend.

The Saudi-led campaign began in March, and the campaign’s spokesperson denied on Monday that the coalition was taking too long to achieve significant advances in the country.

“The US forces and NATO, composed of 28 states, stayed in Afghanistan for 11 years, and they didn’t achieve what the coalition has achieved in seven months.”

Speaking to Saudi daily al-Watan on Monday, Brigadier Ahmed Assiri said the coalition had not announced a timeframe for its operations.

“There is no delay in our military operations – the word 'delay' implies that there is a time frame, but the coalition has never announced a specific date to complete the liberation of Taiz.”

The city of Taiz in southern Yemen has been blockaded by Houthi forces for months, and the Saudi-led coalition alongside local fighters has been attempting to break the siege.