SANAA (Reuters) - A bomb blast hit an anti-U.S. protest in northern Yemen on Friday, injuring at least 22 people, a rebel group that controls much of the north of the country said.
In a statement, the leader of the Houthi movement - Shi'ite rebels that Yemen's military tried to crush in campaigns in 2004-2009 - said the bombing took place in the province of Saada, on Yemen's northwestern border with Saudi Arabia.
It did not say who it believed carried out the attack.
The region has seen bouts of fighting in recent months between the Houthis and Sunni Muslims espousing puritanical Salafi doctrines influential in Saudi Arabia. The Houthis have accused Riyadh of arming their foes.
The conflict with the Houthis is one of several facing Yemen's new president, Abd-Rabbu Mansour Hadi, as he tries to implement a power transfer backed by Riyadh and Washington.
Al Qaeda's active Arabian Peninsula branch is based in Yemen, and claimed responsibility for a suicide bombing in southern Yemen that killed at least 26 people last Saturday, the day Hadi was sworn in.
The transition plan is aimed at averting civil war among an army divided between foes and allies of former President Ali Abdullah Saleh.
Mass protests against him last year were coupled with fighting between pro- and anti-Saleh units. Saleh eventually became the fourth veteran Arab leader unseated by "Arab Spring" protests.
A key element of the plan is restructuring Yemen's military, which the United States wants as a reliable resource in its campaign against al Qaeda in Yemen, a group Washington fears could thrive amid Yemen's political turmoil.
John Brennan, the U.S. "counter-terrorism" chief, has called for a united Yemeni army to carry out that campaign, and the Houthi leader Abdelmalek al-Houthi said the protest was against similar remarks made recently by the U.S. ambassador in Sanaa.
The transition plan calls for Hadi and an interim government made up of Saleh's party and opposition blocs to lead Yemen to elections and write a new constitution within two years.
The plan did not include the Houthis, who have held talks with the U.N. envoy attempting to implement the deal aimed at bringing them into a political process.
(Reporting by Mohammed Ghobari; Writing by Joseph Logan; Editing by Rosalind Russell)