SANAA, Yemen — The Yemeni leader who resigned the presidency last month and fled to the country’s south Saturday said all actions taken since Shiite rebels stormed the capital last September are illegitimate, hinting that he will seek to reclaim his power and office.

The move exacerbates worries over a regional breakup and further instability in the volatile country, the Arab world’s poorest and home to a powerful al-Qaida affiliate. The rebels, known as Houthis, control the capital of Sanaa and several major cities, while the south is largely free from their rule. Officials there have rejected the rebel takeover amid talk of a potential secession.

In a statement signed as “president of the republic” from the southern port city of Aden, Abed Rabbo Mansour Hadi called for a national dialogue there or in the city of Taiz, another area not under Houthi control, and demanded the rebels leave Sanaa.

He said he supports the power transfer plan backed by Gulf countries after Yemen’s 2011 Arab Spring uprising, which envisaged him taking office from predecessor Ali Abdullah Saleh until elections.

He also called on military and security forces to support him, and demanded the Houthis release members of his former Cabinet who are still under house arrest in Sanaa.