Story highlights One car bomb hit Houthi militants; another exploded next to a school bus, officials say

Both bombs, apparently from al Qaeda fighters, were meant for Houthi militants, officials say

Houthis, al Qaeda have been fighting in Yemen for months

Two car bombs killed at least 31 people, including 20 children, in central Yemen's Radaa city when suspected al Qaeda fighters targeted Houthi militants Tuesday, senior security officials and locals told CNN.

One car bomb struck a Houthi gathering point, but the other did not make it to the target and instead blew up next to a bus that was carrying children home from school, officials said.

All the killed children were under the age of 12, said Osama Sari, a prominent pro-Houthi activist.

Eleven Houthi fighters were killed, an Interior Ministry official said.

Eyewitnesses told CNN that the death toll within Houthi lines exceeded 18. At least a dozen others were injured, among them six in critical condition, medical sources in Radaa told CNN.

Radaa was an al Qaeda stronghold that fell to Houthi fighters after clashes in October that killed hundreds from both sides. Al Qaeda has since intensified its attacks on Houthi targets, conducting daily attacks killing hundreds of Houthis and innocent civilians.

Houthis follow the Zaidi sect of Islam and are considered Shiite Muslims by al Qaeda, a Sunni Muslim terrorist network.

Sari said that most of the killed were children and that the attack holds the hallmarks of al Qaeda.

"The suicide car bombs were supposed to directly hit the Houthi camp. When they failed to reach the core target, many innocent children lost their lives," Sari said.