Two suicide car bombers rammed their vehicles into a Shiite rebels' checkpoint and a house south of the Yemeni capital Tuesday as a school bus was traveling nearby, killing at least 25 people including at least 15 primary school students, according to the Yemeni government, rebels and witnesses.

Witnesses said that the first car was loaded with potatoes apparently disguising explosives underneath. When the car bomber arrived at the checkpoint manned by rebels, he blew up the vehicle as the students' bus was passing. After the first explosion, a second car targeted the home of a Shiite rebel leader, Abdullah Idris.

The Defense Ministry said in a statement that at least 25 people were killed in the twin bombings, however the Interior Ministry later said three children were killed and 37 wounded with eight in critical condition. It was impossible to independently confirm the casualty figures.

Witnesses at the site of the attack said that the rebels brought four pickup trucks and dumped dozens of bodies into them while several ambulances rushed to the scene to carry away the wounded. Body parts littered the street along with open bags of potatoes.

The Shiite rebels, known as the Houthis, blamed al-Qaida for the attack in the Radaa area of Baydah province, calling it "the ugliest crime against childhood." The group said the school bus was carrying female primary school students.

The witnesses spoke on condition of anonymity.

This is the second time Idris's house has been targeted since October. The Houthis and al-Qaida have been fighting in Radaa since the rebels overran the area in October.

The empowered Shiite rebels have made significant military advances in recent months, seizing control of the capital and other strategic cities.

Yemen has been gripped by a power struggle between President Abed Rabbo Mansour Hadi and the Houthis, who have allied with his predecessor, ousted President Ali Abdullah Saleh. On Tuesday, Saleh loyalists, who form the majority of parliament, derailed a vote of confidence on the new government's program. A raucous session Tuesday came to an abrupt end before a vote, after Saleh loyalists bickered over internal party politics.

They accuse Hadi of backing U.N. sanctions against Saleh and two top rebel leaders, and have called on the government to explicitly denounce the sanctions.

Also Tuesday, Shiite rebel gunmen, who seized control of Sanaa in September, surrounded the ministry of defense and packed the city's nearby streets, preventing the minister from accessing his office. A day earlier, the minister had kicked out the rebels from around the ministry for blocking his chief of staff from entering.

Later, Hadi drove to the ministry, effectively ending the siege.