KABUL, Aug 30: A heavy security clampdown was enforced on Monday in the Afghan capital after the bombing of a US firm left at least nine people dead, including three Americans , and raised new fears about security just weeks before the country's historic elections.

Sunday's attack on security contractor DynCorp was claimed by spokesman linked to the Taliban and Al Qaeda, and analysts said more attacks could be expected in the run-up to the Oct 9 polls.

A truck loaded with wood and packed with explosives was detonated outside DynCorp's office in the Shar-i-Naw district, home to many aid agencies and foreign firms. DynCorp provides Afghan President Hamid Karzai's bodyguards and trains the fledgling police force.

Ken McKillop, spokesman for the NATO-led peacekeeping force, said that three US citizens and three Afghan nationals treated by the International Security and Assistance Force (ISAF) had died in the attack.

However, the spokesman said he could not comment about casualties who may have been taken to other medical facilities in the city and could not confirm the total death toll from the attack.

The Afghan government said on Sunday that three Nepalese citizens also died in the attack. A Western security source also confirmed that three Nepalese were among the dead.

The attack was the worst in Kabul since Dec 28 last year and the second major bomb attack over the weekend. At least 10 people, most of them youths, died when a bomb exploded at a religious school in southeastern Afghanistan on Saturday

US troops on Monday patrolled the streets of the Wazir Akbar Khan district, home to the US and many other foreign embassies. The streets were snarled with traffic caused by the many roadblocks.

In the Shar-i-Naw district, the streets leading to the blast site were blocked off and large numbers of NATO-led peacekeeping troops backed by tanks patrolled the streets.

Shar-i-Naw is packed with United Nations offices and the headquarters of many other aid agencies. Afghan police were stationed outside UN offices waving away vehicles and preventing them from stopping.

The US embassy and other Western governments have asked their staff to restrict their movements and avoid crowded shopping streets and restaurants popular with foreigners for fear of another attack.

"This was a well-predicted attack and a well-chosen target. I think it's prudent to expect to see more. We anticipate possibly a series and a campaign of attacks," said Nick Downie, security coordinator for the Afghanistan NGO Security Organisation.

The Afghan capital has been bracing itself for a large-scale bomb attack in recent weeks in the run-up to the elections. Afghan intelligence officials supported by NATO-led peacekeeping troops found 530 kilograms of explosives as well as detonating devices and arrested two militants last week in a district on the outskirts of Kabul.

Two people were arrested on Saturday for carrying 2,000 pro-Taliban leaflets near the Afghan-Pakistan border, officials said. As the elections have drawn closer, security across the country has worsened and a string of attacks on election workers has left 12 dead since May.

Reconstruction firms, the United Nations and aid workers have also been targetted in recent months. The Taliban have vowed to disrupt the polls, in which over 10 million people have registered to vote. -AFP