SANAA, Yemen — Yemeni Shiite rebels, making an aggressive bid for power in the impoverished Gulf state, arrested more than a hundred members from a rival Islamist Sunni political party, including two leaders, the party said in a statement Sunday.

The Islah party, the Muslim Brotherhood’s branch in Yemen and a traditional power player in Yemen, had declared its support for the Saudi-led coalition bombing campaign against the rebels and their allies. The Shiite rebels, known as Houthis, have been joined by security forces loyal to the ousted President Ali Abdullah Saleh — whose loyalists control elite forces and large combat units in Yemen’s military.

The Saudi-led campaign in its 11th day aims to thwart the advances of the rebels, who took over the capital Sanaa in September and eventually forced President Abed Rabbo Mansour Hadi to flee to Aden, Yemen’s second largest city in the south, after putting him under house arrest. The combined force of Houthis and Saleh loyalists is now advancing on Aden and seeking to tighten their hold on this nation of 25 million on Saudi Arabia’s southern border. Hadi has since fled to Saudi Arabia, and the coalition campaign has yet to stop the rebels’ push to take control of the south.

The overnight arrest campaign rounded up leading members of the Islah party, Mohammed Qahtan and Hassan al-Yaeri, along with more than 120 others, the group said in a statement on its website. Also on Sunday, medical officials said coalition airstrikes in Dhale, a southern city the rebels are trying to control in order to open a corridor to Aden, killed at least five civilians, apparently when an errant missile hit a residential area.