Could a new front be opening up in the war on terror?

The deadly car bombing outside the US embassy in Yemen represents an escalation in attacks against Western targets and shows al Qaeda-inspired jihadis are growing in ability and determination.

Islamic Jihad has claimed responsibility for the attack, which killed at least 16 people, but it is possible that other groups will come forward in the next few days.

There is a complex network of over-lapping splinter cells and claims of rival leadership within Yemen.

Extremist violence in Yemen has been on the rise since February 2006, when 23 prominent militants tunnelled their way out of a high-security jail.

Ten Europeans and four Yemenis have died in attacks on tourist convoys in the past 15 months.

In March, a misfired mortar strike hit a girls' school next door to the US embassy by mistake.

A subsequent bombing campaign in the capital - against an expatriate residential compound and oil company offices - prompted the US state department to evacuate all non-essential embassy staff from Yemen.

US employees had just started to return to their embassy desks at the end of August - so the timing of the latest attack is significant.

Crackdown

During July, Yemeni security forces killed five al-Qaeda suspects, disrupted a second cell and arrested more than 30 suspected al-Qaeda members.

But this attack shows that effective leadership remains intact and operational capacity has not been disrupted.

Two Saudi passports were found among documents seized in the July raids and interrogations were said to have uncovered plans to launch attacks in Saudi Arabia and Yemen. Yemen subsequently extradited eight Saudi nationals to Riyadh.

The raids underlined the importance to Saudi Arabia of Yemen's internal security. But Yemen is also paying the price for the northern kingdom's muscular clampdown on its own insurgents.

In March, a Saudi militant fundraiser said al-Qaeda had been defeated in Saudi Arabia and he called on his remaining associates to flee to Yemen to escape capture or assassination by the Saudi authorities.

The current migration of Saudi jihadis to Yemen coincides with the emergence of a transnational structure calling itself al-Qaeda in the South of the Arabian Peninsula.

Yemen's mountainous terrain and the weak presence of state structures outside Sanaa have long fostered close ties between jihadis in these neighbouring states.

 From BBC News