Air strike in Sanaa, Yemen
A Yemeni man stands amid the ruins of buildings destroyed in an airstrike by the Saudi-led coalition in the capital, Sanaa, Sept. 10, 2015. Mohammed Huwais/AFP/Getty Images

SANAA (Reuters) - At least nine Yemeni civilians were killed in air strikes by Saudi-led warplanes that targeted the home of a leader in the dominant Houthi movement in the capital Sanaa, medical sources said on Thursday.

The leader, Ibrahim al-Shami, was not in the house at the time.

The air raids by a Saudi-led coalition have intensified in recent weeks as a Gulf Arab ground force and fighters loyal to exiled President Abd-Rabbu Mansour Hadi prepare a campaign to recapture Sanaa, seized by the Houthis in September 2014.

Residents of the Yemeni capital said warplanes made repeated sorties on Yemeni army bases and the vacant homes of relatives of former president Ali Abdullah Saleh, an ally of the Houthis, for several hours on Wednesday night into Thursday morning.

The deadliest attacks were in al-Jaraf neighborhood, in northern Sanaa, where warplanes targeted Sham's home.

Medical sources said some of the victims fell when residents, including a journalist from the Houthi-run al-Masirah television, gathered at the site.

The coalition began air strikes against the Houthis and their allies -- forces loyal to Saleh -- in late March after they pushed from their northern stronghold towards the southern port of Aden.

International human rights groups have expressed concern at the number of civilians killed in the raids.

On Tuesday, the Houthi-run Saba news agency reported that at least 54 people were killed by Saudi-led air strikes on targets across Yemen.

The coalition is currently pushing ahead with an offensive in Marib, about 120 km (75 miles) east ofSanaa, trying to drive the Houthis out of the province in preparation for a push against the capital.

After seizing Sanaa, the Iran-allied Houthis eventually forced Hadi and his administration to flee toSaudi Arabia.

Yemeni Vice President and Prime Minister Khaled Bahah and his cabinet returned to Aden on Wednesday, saying they intend to run the country from there until they can go back to Sanaa.