SANAA (Reuters) - Two al Qaeda-linked suicide bombers targeting Shi'ite Muslims blew themselves up at a school and a protest march in northern Yemen on Friday killing at least 12 people, the defence ministry said.
The attacks came less than a week after a suicide bomber in army uniform detonated an explosive belt at a military parade rehearsal in Sanaa, killing more than 90 soldiers and wounding at least 200 more.
The United States and its Gulf Arab allies have watched with mounting alarm as al Qaeda-linked militants, emboldened by political instability in Yemen, have launched a series of audacious attacks in the impoverished state.
A militant Sunni Islamist group affiliated to al Qaeda said it had carried out both attacks in revenge for the killing of fellow Sunni Muslims in Yemen's north, a Shi'ite rebel stronghold bordering Saudi Arabia.
Sunni Muslim militants affiliated to al Qaeda view Shi'ite Muslims as heretics.
One attack occurred in the northern al-Jawf province, where a suicide bomber drove into a school in which members of a Shi'ite rebel group, also known as Houthis, had gathered to pray, killing 12 people, a local official said.
An offshoot of Ansar al-Sharia (Partisans of Islamic Law), itself an affiliate of al Qaeda's Yemen-based wing, said more than 20 Houthi "apostates" had been killed, in a statement claiming responsibility for the attack.
Earlier on Friday, another suicide bomber targeted a Houthi protest march in the rugged northern province of Saada, where the rebels have effectively carved out their own state within a state. There were no casualties in the attack, the Houthis said in a statement.
"As the march was taking its first steps, the suicide bomber, who was wearing an explosive belt, tried to breach the security barriers and enter the square," read a statement from the Houthis' media office.
"But those responsible for protecting the protest stopped and searched him, which made him nervous and he lost control, blowing himself up erroneously..."
The al Qaeda-linked group put the death toll at more than 20.
Washington is trying to counter the threat of Islamist militants by deepening its involvement in Yemen, using drone strikes to target suspected militants and training the Yemeni army to fight them.
Islamist militants in Yemen have so far focused on attacking troops sent to fight them in the south of the country, where they control several towns in the southern Abyan province, but the group warned the Houthis they were also targets.
"O apostates, don't think that we have forgotten you or that out battle against the crusaders and their allies in Abyan will stop us from fighting you. For, by God, we will not cease until we purify the Arabian Peninsula of you," it said.
The Houthis have fought regularly with Sunni Muslim Salafis attending a religious college in Saada. They accuse Riyadh of smuggling weapons to the Salafis because the two follow a similar creed.
Saudi Arabia briefly fought the Houthis in north Yemen after they grabbed Saudi territory in 2009.
The U.S. envoy to Yemen said in February there were signs that Shi'ite Iran was becoming more active in Yemen and could pose a deeper threat to its stability and security. Iran denies interfering in the country.
(Reporting by Mohammed Ghobari; Writing by Isabel Coles; Editing by Michael Roddy)