The truce put an end to violence in a civil war that has raged on and off since 2004.

The official told Reuters the rebels were held in prisons in Sanaa and Saada in northern Yemen. He said more would be freed in the coming days, without providing figures.

A Qatari delegation met Yemeni President Ali Abdullah Saleh in Aden this week to discuss the peace agreement, the official said. "(Qatar's) efforts being exerted at the moment are fruitful," he said, speaking on condition of anonymity.

The official said the Houthis would return equipment seized in confrontations with the government as part of the peace deal.

Rebel spokesman Mohammed Abdul Salam told Reuters that 426 prisoners were released Thursday.

Qatar brokered a Yemen peace accord in 2008 before the region slipped back into war. Yemen faced international pressure to resolve domestic conflicts in order to focus on Al-Qaeda.

Aside from the Houthi rebels in the north, Yemen is struggling to combat a resurgent wing of Al-Qaeda and a separatist rebellion in the south.