An insurgent group which has been fighting the government for many years in northern Yemen has taken control of most of a city near the Saudi border, diplomatic insiders said on Thursday.

Ali Abdullah Saleh is struggling to contain a nationwide movement demanding his resignation as president.

Faris Mana’a, a member of a prominent local family, said the governor of the area had fled and he was now in charge.

“Control over the Sa’ada governorate and its capital have been achieved for the sake of toppling this regime,” Mr Mana’a told the Financial Times.

According to people familiar with the situation on the ground, fighting between the Houthi insurgent group and tribesmen loyal to the government has been taking place over the past few days in the northern governorate of Sa’ada, and the rebels took control of most of the capital, Sa’ada City, on Wednesday.

Sana’a opposition dismiss Saleh offer to go

Yemen’s opposition stepped up efforts to remove President Ali Abdullah Saleh on Thursday, dismissing his offer to stand down after a presidential election at the end of the year, reports Reuters.

Tensions ratcheted higher a day ahead of a planned rally that protesters have dubbed “Friday of Departure”, and presidential guards loyal to Saleh clashed with army units backing opposition groups demanding his ouster.

But a top general who has thrown his weight behind the protesters said he had no desire to take power, as fears grew of a major confrontation between rival military units in the capital Sanaa or elsewhere.

The government was unable to confirm or deny the reports.

Although the Houthi group has expressed support for the anti-government popular protest movement that has been gaining ground in the country since the downfall of Hosni Mubarak, the Egyptian president, it has its own long-standing conflict with the government.

Analysts said the significance of the move was primarily as an indicator of the weakness or distractedness of the beleaguered regime.

The position of Mr Saleh has become increasingly fragile since gunmen opened fire on anti-government protesters last week, in a massacre that left more than 50 dead and triggered the defection of powerful generals.

The Houthi group, who adhere to an offshoot of Shia Islam, has been fighting an on-off insurgency with the government since 2004. The origins of the conflict are murky but the emergence of Saudi-backed Sunni Salafists in northern Yemen is said to have been a factor.

Saudi Arabia intervened militarily in the conflict at the end of 2009 when Houthi fighters killed a Saudi border guard, launching air strikes on rebel positions before a ceasefire was agreed in early 2010.

According to Hassan Zaid, an opposition party leader with links to the Houthi group, army units still remain in the area. Sa’ada is part of the military district commanded by General Ali Mohsen Al Ahmar, who on Monday expressed his support for an anti-regime protest movement.

It was unclear how long the Houthis would be able to hold on to control of the city. “Ali Abdullah Saleh has other problems,” said one western diplomat. “They will handle that later on.”

Authorities in Dubai said on Thursday they had apprehended a shipment of 16,000 guns bound for Yemen.

Clashes were reported to have taken place in many of Yemen’s tribal areas, prompting fears that the volatile political situation could descend into violence.

William Hague, the UK foreign secretary, told parliament that he was reducing the embassy in Sana’a to all but a core staff because of the deteriorating security situation. He told all British nationals remaining in Yemen to leave “without delay.”