Qatari mediators returned to Yemen's volatile northern province of Saada on Sunday, hoping to salvage a truce brought to the verge of collapse by a mosque bombing and days of clashes between rebels and the army. Rebels led by Abdul-Malik Al-Houthi seized a government building in the town of Manbah after clashes on Saturday and the army has now surrounded the compound, local tribal sources said. Tribes were mediating an end to the standoff. “The Qataris and the government delegation have now returned to Saada amid continued to tensions,” said Saleh Habra, the chief rebel negotiator. The situation in Saada remained tense after a bomb planted in a motorcycle killed 15 people outside a mosque on Friday, with government forces setting up checkpoints around the city and few people on the streets, he said. Yemen has witnessed attacks by different groups targeting everything from tourists to government offices in recent years, but attacks on mosques were virtually unheard of until Friday. A security source said several suspects had been detained at a checkpoint in Saada on Friday and investigations suggested that followers of Houthi were behind the attack, a charge Houthi denies. Fighting has raged on and off in Saada since a conflict broke out in 2004 between government forces and the Zaydi rebels which Houthi now leads. A Qatari-brokered truce ended six months of intense fighting in June but violence has increased in recent weeks as a lack of trust on both sides and disagreements over the release of prisoners and handover of arms threaten to undermine the deal. The Qatari mediators face a tough task salvaging the deal with both sides claiming the other side is not serious about making peace. The rebels are worried that if they give up their weapons and prisoners first, they will be attacked. The government is reluctant to release its prisoners since a state amnesty that freed 600 rebels in 2006 failed to end the revolt. Hundreds of people have been killed and thousands have fled their homes in Saada since the conflict began.