The United Nations refugee agency has suspended aid work in parts of eastern Afghanistan after two of its security guards were killed in an attack on a convoy.

Gunmen attacked the UNHCR convoy as it was travelling through Nangarhar province, about 40 kilometres (25 miles) west of Jalalabad, on Sunday.

Three policeman and a suspected attacker were also reported killed.

Aid work has been suspended in the Sherzad, Hisarak and Khogyani districts, a UNHCR official in Geneva told BBC News Online.

The UNHCR hopes to lift the suspension within the next few weeks.

A spokesman in Kabul said the suspension meant refugees would not be receiving basic needs, like shelter and clothing.

Fire-fight

The attack happened when the UN convoy spotted a body in the road.

When the security guards investigated one was shot dead.

The driver and second security guard tried to flee but were also shot.

Opium disputes may have been to blame

The second guard died later in hospital.

General Abdul Malik Malikzai, who heads the 4th Brigade of the Afghan army in Jalalabad, told the AP news agency on Monday that three policemen were also found dead at the site.

One of the suspected attackers was also killed, he said.

A second was wounded and was being questioned.

The two security guards killed were privately-hired and not UN staff members.

General Malikzai said Afghan authorities believed one of the attackers was Maulvi Hamdullah, who is suspected of links with the Taleban.

Appeals hampered

BBC correspondent in Kabul Kylie Morris says the district where the attack happened is notorious for banditry and the growing of opium poppies.

A UN source told the BBC the attack may have resulted from tensions connected to the current ban on opium production and disputes between local commanders.

The attacks will hamper President Hamid Karzai's appeals for more international assistance.

In the past year more than 1.2 million Afghan refugees have returned to their homeland, taxing Mr Karzai's government as well as the United Nations.