A car bomb claimed by ISIS exploded in the Yemeni capital Sanaa overnight on Monday, medics said, wounding at least 28 people gathered to mourn another attack earlier this month that killed Shia Houthi rebels.

"The explosion was caused by a car bomb which exploded behind the military hospital in the Sha'oub district in Sanaa, which injured 28 people including 12 women in a building where victims of a previous attack were being mourned," a medical source said.

Security officials said the blast in Sanaa targeted the homes of several Houthi leaders. Houthis cordoned off the area after the explosion and prevented anyone from entering as ambulances rushed to the scene.

"At approximately 11:30 we heard a loud explosion," witness Yehia Ali said. "It was a truly powerful explosion. … It was an explosive placed inside a car. The car was an Echo that had been parked here since about eight in the evening and no one paid attention to it."

The fighting pits Shia Houthi rebels and allied fighter loyal to former president Ali Abdullah Saleh against southern separatists, local and tribal militias, Sunni militants and loyalists of the exiled president.

The rebels seized the capital in September. In March, a Saudi-led and U.S.-backed coalition began launching airstrikes against the rebel forces. The political vacuum has given hard-line Sunni militants, who regard the Houthis as apostates worthy of death, greater room to operate.

In a new sign the conflict was ratcheting up, the country's military spokesman said its forces had launched a Scud missile at a Saudi military base overnight Monday.

In a statement posted online, ISIS claimed responsibility for the blast, saying it had targeted the area "out of revenge for the Muslims against the Houthi apostates."

Despite the months of Arab airstrikes backing up the Houthis' armed opponents in Yemen, the rebels have not lost ground on the battlefield and have stepped up their exchanges of artillery and rocket fire with Saudi forces along their border.