At least 20 people have been killed and 50 others injured in a suicide bomb attack on a construction company  in eastern Afghanistan, local authorities said.

The Taliban claimed responsibility for the blast, which occurred late on Sunday in the remote Bermel district of Paktika province.

"The attacker smashed a car laden with explosives into the construction company building," Mokhles Afghan, spokesperson for the provincial governor, told the AFP news agency of the attack.

He said that engineers, construction workers and security guards were among those killed in the blast in the restive eastern province, which shares a long, porous border with Pakistani areas troubled by Taliban fighters.

The Afghan interior ministry said the attackers used a truck carrying a large amount of explosives. They shot their way into the company's compound before detonating the bomb, a statement from the ministry said.

Taliban claim

In an emailed statement to media, Taliban spokesman Zabihullah Mujahid said the group had carried out the attack but said it had been on a military base and that 49 foreign and Afghan troops had been killed and wounded.

However, local officials in Paktika said the dead and wounded included employees of the firm and other civilians.

Civilians are increasingly getting caught up in the violence that has blighted Afghanistan since a US-led invasion in 2001 ousted the Taliban, triggering an insurgency whose intensity has increased in recent years.

The United Nations said that last year was the deadliest for civilians since the conflict began, with 2,777 killed - a 15 per cent increase on 2009 figures.

Three-quarters of these deaths were caused by attacks linked to the insurgents.

Sunday's attack underscores the huge security challenges Afghanistan faces, less than a week after president Hamid Karzai announced that local military and police will take over from NATO in seven parts of the country this summer.

The move, nearly 10 years after the US-led invasion in the wake of the September 11 attacks, is the first step towards the withdrawal of foreign troops from Afghanistan by the end of 2014.

Source: Al Jazeera and agencies