Gunmen blew up a voting station on Monday in southern Yemen, one day before the country is to go to the polls to rubber stamp its vice president as the new head of state.

The attack in the port city of Aden underlines the security vacuum in the Arab world's poorest country after a one-year popular uprising seeking to oust longtime President Ali Abdullah Saleh.

Under a U.S.-backed deal brokered by Yemen's Gulf Arab neighbors, Saleh's deputy, Abed Rabbo Mansour Hadi, is to become president after a vote Tuesday in which he is the only candidate.

Posters and huge banners brandishing Hadi's photo and urging Yemenis to vote have appeared throughout the capital Sanaa as the vote approaches. Thousands of people attended an electoral rally early Monday in support of Hadi.

Hadi, a low-profile figure who has served under Saleh for years, did not attend the event and has rarely addressed the public. Still, many Yemenis who originally opposed the deal that will bring Hadi to power now support the move merely because it will officially end Saleh's 33-year rule.

Security has collapsed across Yemen during the uprising, with security forces regularly using lethal force against protesters and clashing with various armed groups. The U.S. and Saudi Arabia have struggled to ensure a smooth transition in hopes that Yemen will continue to cooperate in fighting the country's al-Qaida branch, which has carried out attacks in the U.S.

The militants have exploited the unrest in Yemen to seize territory in the country's south.

It was unclear who was behind Monday's attack on the polling station in Aden.

A security official said gunmen fired a rocket-propelled grenade at the station, then fled. No one was hurt, and police are searching for suspects, the official said, speaking on condition of anonymity in line with security regulations.