He is expected to report his findings to Barack Obama, the US president, who wants the Pentagon to focus on combating Taliban and al-Qaeda linked fighters based in Pakistan and Afghanistan.

Taliban assault

Taliban fighters launched one of their most audacious raids on Kabul to date on Wednesday, killing 20 people in a co-ordinated assault on three government buildings.

In video

Security in focus as US envoy visits Afghanistan

Taliban in deadly Kabul attacks

Hamish MacDonald, Al Jazeera's correspondent in Kabul, said: "The information we are getting is that the events of Wednesday would have no bearing on Holbrooke's travel plans.

"But clearly, if those events are not affecting his plans, they will certainly affect the meeting he will hold. He will surely be asking leaders here why they cannot even secure government infrastructure in the capital."

Afghan intelligence officers say they are investigating links between Pakistan and Taliban fighters who carried out the raid.

"As they were entering the ministry of justice before starting their indiscriminate killing of the civilians in there, [the attackers] sent three messages to Pakistan calling for the blessing of their mastermind," Amrullah Saleh, an Afghan intelligence chief, said.

Mumbai parallel

The three raids on two ministries and a prisons department office were a new tactic by the Taliban, who have previously only attacked a single target at a time.

"These suicide bombers were not the ordinary Taliban type of suicide bombers who come and blow themselves up somewhere," Haroun Mir, a political analyst and co-founder of the Afghanistan Centre for Research and Policy Studies, told the Reuters news agency.

"They had rifles as well and their aim was not to immediately explode themselves.

"It was, in my opinion, to take hostages and continue the way they did in [November's attack on] Mumbai, to paralyse Kabul and hopefully inflict a big blow to Holbrooke's trip."

Deployment debate

Obama is expected to approve the deployment of about 30,000 extra troops to Afghanistan in the next few days.

The force is seen as vital for securing presidential elections - only the second in Afghanistan's history - set for August 20 after being postponed for three months largely because of security concerns.

The US administration has made improving security in Afghanistan a priority [AFP]
In Washington on Thursday, Al Jazeera's Anand Naidoo asked Robert Wood, the US state department spokesman, if the deployment is likely to go ahead.

"The president has made it very clear that Afghanistan is going to be a priority and that we need to do more in terms of fighting the Taliban," Wood said.

"And so, once a decision is made to deploy additional forces that'll be announced. But I don't have any additional information at this point."

Xenia Dormandy, a former South Asia section head at the US National Security Council, told Al Jazeera: "There is a debate because they truly do not know what the border Afghan policy is going to be over the coming years.

"They are still trying to decide what are going to be the objectives over the next year to two years. And until the new administration comes up with these new objectives, the question of how many forces and how much US forces you need is very much up in the air."