Hamid Karzai, the Afghan president, is preparing to announce an official timetable for the withdrawal of foreign troops from his country, a British newspaper has reported.

International forces fighting in Afghanistan are set to agree to hand over control of security in the country to Afghan forces by 2014, The Independent on Sunday reported, citing leaked documents.

Karzai is expected to announce the timetable for a "conditions-based and phased transition" at an international security conference in Kabul, the Afghan capital, on Tuesday.

"The international community expressed its support for the president of Afghanistan's objective that the Afghan National Security Forces [ANSF] should lead and conduct military operations in all provinces by the end of 2014," the document read, according to the paper.

Cautious approach

However, Joe Biden, the US vice-president, took a more cautious approach in remarks the planned US military drawdown in Afghanistan next July.

He told ABC television's "This Week" on Sunday that the number of US troops leaving Afghanistan "could be as few as a couple of thousand troops".

Barack Obama, the US president, ordered 30,000 more troops to Afghanistan last December, bringing the US total to about 100,000.

Biden said it is still too early to determine whether the US strategy in Afghanistan will succeed, but he said there is progress.

Al Jazeera's Zeina Khodr, reporting from the capital, said security will be among the issues discussed at Tuesday's gathering of Afghanistan's international partners.

"Particularly when the Afghan government plans to eventually take over security," she said.

"More than 70 international representatives, including some 40 foreign ministers will be listening to the Afghan government's plan on how they intend to do that."

Afghan and foreign forces have stepped up security ahead of the conference, with the deployment of thousands of additional forces on the streets.

Despite the increased efforts, three people were killed and at least 30 others injured on Sunday when a suicide bomber detonated explosives in central Kabul.

'High infiltration'

Afghan officials said the bomber may not have reached his intended destination due to tight security.

"He was trying to get to a specific area but because of high security the bomber was forced to detonate on a street where there is little activity," Zemarai Bashary, a spokesman for the interior ministry, said.

Haroun Mir, the co-founder and deputy director of Afghanistan's Centre for Research and Policy Studies, in Kabul, said there is a huge risk that the conference could be disrupted by another such attack.

"There is a high level of infiltration by the Taliban inside the Afghan security forces," he told Al Jazeera.

"In a number of attacks, Afghan officers were involved in helping the Taliban and other terrorist networks in executing these attacks.

"This is something the Afghan security forces are unable to prevent."