Bicycle bombers kill four in east Afghanistan

Two suicide bombers on bicycles killed four people and wounded 31 in Afghanistan's eastern Laghman province today, provincial officials said.

The attacks come after a spike in violence over the past week and as NATO leaders gather for a second day at a summit in Lisbon where they will discuss plans to start transitioning security responsibility to Afghans.

The first bomber detonated his explosives at a police checkpoint in Alisheng district and the second struck several hundred metres further back, Provincial Governor Mohammad Iqbal Azizi told Reuters.

Taliban spokesman Zabihullah Mujahid said the hardline Islamist group had carried out the attack and that the target had been Afghan police and intelligence officials.

"We are not sure what the target of the second bomber was but we think he may have detonated his explosives prematurely," Azizi said.

A string of recent attacks are a reminder of the massive and growing military challenge posed by the Afghan insurgency, as US President Barack Obama and his administration gear up for a review of the war strategy in December.

Civilian and military casualties this year have been the highest since the 2001 overthrow of the Taliban, despite the presence of around 150,000 foreign troops, and violence has spread to previously peaceful northern provinces.

Last Saturday, Taliban fighters, including at least two suicide bombers, attacked a foreign military base in Jalalabad at the main airport in eastern Afghanistan, one of four incidents in 24 hours, that marked an sudden upswing in violence.

On Monday, the NATO-led force said five of its troops had been killed over the weekend in a clash with insurgents in Kunar province, also in the east. It was the deadliest attack on foreign troops in six months.

At least 2,224 foreign troops have been killed since the start of the war, more than 650 of those in 2010, making it the deadliest year of the war so far.

But civilians have borne the brunt of the fighting as they become caught up in the crossfire. According to the UN figures, 1,271 ordinary Afghans were killed in the first six months of this year, a 21 per cent jump on the same period in 2009.