JEDDAH – Saudi troops exchanged fire with snipers from Yemen Shi'ite rebels who have crossed over the border, a Saudi military source said on Sunday, days after the rebels said they had withdrawn from Saudi land. Saudi Arabia declared victory over Yemeni Shi'ite rebels on Wednesday following a ceasefire offer from the rebels. The world's top oil exporter was drawn into a conflict between Yemen's government and the rebels in November, when Riyadh launched a military assault against the insurgents after they seized some Saudi territory. "The snipers are still present," a Saudi military source told reporters, adding that exchange of fire was happening on a daily basis. "These people cannot be trusted, every day they creep in and out, but they do not really pose a threat," he said. Yemen, which earlier this month declared an open war on al-Qaeda and is struggling to contain a secessionist movement in the south, has been fighting the rebels on and off since 2004 but the conflict intensified last summer. Yemen's armed forces have clashed with Shi'ite rebels in the north, killing 20, state media reported yesterday, a day after the insurgents said they accepted the government's terms for a ceasefire. The growing instability in Yemen is a worry to Western powers, who fear the country could become a failed state, allowing al-Qaeda to strengthen its operations there. Britain hosted talks on Yemen in London last week after an attempt to bomb a plane on December 25 on its way to Detroit drew the world's attention to al-Qaeda in Yemen. A rebel group has said it will accept a truce offered by the Yemeni government on condition that the government ends its "unjust war" against it. The possible truce would end sporadic fighting that has lasted for more than five years. "And here, since we are so keen on ending this bloodshed and in order to avoid the catastrophic situation that the country is heading towards and in order to end the acts of genocide against civilians, we renew for the fourth time what we previously announced, our acceptance of the five points that the Yemeni government asked for, after they end the aggression," Houthi rebel leader Abdul Malik al-Houthi said in an audio recording on the group's website. Meanwhile, Yemen has rejected a ceasefire offer from northern Shi'ite rebels, citing the absence of a promise to end attacks on Saudi Arabia, a government official said on Sunday. The offer, made by the rebels' leader on Saturday, was also rejected because rebels were demanding the government end its military operations first, the official said. In August, Yemen laid out cease-fire terms that included removing checkpoints, ending banditry, handing over all military equipment and weapons, and releasing civilians and military personnel. In September, government officials said Houthi leaders twice rejected the terms, while al-Houthi said Saturday that the militants had twice declared they wanted to end the conflict. The revolt by the Shi'ite Muslim Houthis in northern Yemen began in 2004 and has even spilled over into the country's northern neighbour, Saudi Arabia. The conflict is believed to be both separatist – over who will have power in the area – and sectarian – whether Shi'ite Islam will dominate even though the majority of Yemenis are Sunni.