Yemeni President Ali Abdullah Saleh ordered a probe into deadly violence in the capital, Sana'a, Thursday, a day after he agreed to an Arab League plan that calls for him to relinquish power.

Witnesses said five people were killed and at least 34 wounded after Mr. Saleh's loyalists opened fire on protesters who were upset over a provision in his power transfer deal that gives him immunity from prosecution.

Mr. Saleh, who signed a Gulf Cooperation Council plan Wednesday to transfer power to his vice president and hold early presidential elections, condemned the killings and ordered an investigation into what happened.

An Interior Ministry official denied that the government was responsible for Thursday's violence.

Meanwhile, the International Committee of the Red Cross said Thursday three of its aid workers, who were kidnapped by insurgents two days ago in the country's volatile south, have been released.

Yemeni officials blamed the kidnapping on the Southern Movement, a group that wants independence for Yemen's south. The kidnappers were demanding the release of prisoners held by Yemeni authorities.

Kidnappings of Western tourists or aid workers by tribes seeking ransom or concessions from the government have been frequent in Yemen, one of the Arab world's poorest countries. Most hostages have been freed unharmed.

Also, al-Qaida-linked militants have seized control of several parts of southern Yemen as the government has struggled to contain unrest in other regions.