The arrests came days after President Hamid Karzai and US officials warned that foreign fighters were slipping into Afghanistan to cause mayhem ahead of parliamentary elections.
The men, armed with rocket-propelled grenades and assault rifles, were arrested Sunday in the Qarghayi district of northeastern Laghman province, just 150 feet from where Khalilzad had planned to inaugurate a road with Afghanistan's interior minister, two senior Afghan officials told The Associated Press.
The officials said agents were lying in wait after intelligence forces were tipped off about the plot in advance. Khalilzad, who is to be the next US ambassador in Iraq, canceled his appearance at the road opening at the last minute and was never in danger. The interior minister, Ali Ahmad Jalali, also canceled his appearance.
Presidential spokesman Jawed Ludin confirmed the arrests, and Deputy National Security Director Abdullah told privately owned Tolo TV that the men were all between the ages of 19 and 23.
Afghan television broadcast a video of the suspects in custody -- all wearing traditional shalwar khameez and sporting thin mustaches -- sitting on a brown sofa and being questioned by a man off camera. They identified themselves as Murat Khan, Noor Alam and Zahid and said they were from Pakistan.
None confessed on camera or was asked any questions about the planned attack.
But the two senior officials said the men had admitted their guilt to intelligence agents and told authorities they were in Afghanistan "to fight jihad," or holy war.
The officials, both of whom have intimate knowledge of the investigation, spoke on condition of anonymity because of the extreme sensitivity of the intelligence and their positions within the government.
"Their aim was to assassinate Khalilzad, and they came to Afghanistan specifically for this operation," said one of the officials.
A State Department official, who declined to be identified because he is not authorized to speak for the department, confirmed that the assassination attempt had been thwarted but gave no details.
He said several plots against Khalilzad, Karzai and other senior officials had been foiled, but he didn't give details.
Khalilzad, 54, became America's top diplomat in Afghanistan in November 2003 after serving as Washington's special representative here. Born in Afghanistan, he studied at the University of Chicago and has long been involved in crafting Washington's policy on the region.
Khalilzad has not shied away from offering his opinion about Afghan political players, earning a reputation as the true power behind the US-backed Karzai. He has also repeatedly criticized Pakistan, prompting official protests from Islamabad.
Khalilzad to lead search for new Iraq regime
News of the plot comes after three months of unprecedented bloodshed across the south and east. At least 280 rebels and 29 US troops have been killed since March.
On Monday, fighting between Taliban militants and Afghan security forces left 18 insurgents and five others dead, a day after the US military pounded suspected rebels in airstrikes that killed as many as 20.
The spike in fighting has raised fears that the Afghan war is widening as the nation gears up for September parliamentary elections. Khalilzad himself warned on Thursday that the vote would be a likely target of insurgents.
It was not immediately clear who sent the men, but one of the Afghan officials said the fact the plotters knew details of Khalilzad's trip, and were aware that Jalali was supposed to be with him, was "very disturbing." "We don't know how they got this information," he said.
One of the officials said the Afghan government was extremely angry at what he called a lack of cooperation from Pakistan in stopping militants from crossing the border. He said Islamabad's lack of resolve was a factor in both the assassination plot and the recent surge in violence.
Pakistani Information Minister Sheikh Rashid Ahmed reacted angrily to any hint of official sanction for the attack.
"This is a baseless allegation," he told AP. "Pakistan is not involved in any such thing, now or in the past."
Afghan officials say privately they believe some elements of the Pakistani army and intelligence network are helping Taliban and al-Qaida fighters.
Pakistan vehemently denies the charges. Officials boast that they have stationed tens of thousands of troops along the border and arrested more than 700 al-Qaida suspects.
But officials here say Pakistan wants US troops out of Afghanistan, a country Islamabad has historically seen as lying within its sphere of influence. Privately, members of Karzai's government express frustration that Washington has not taken their warnings about Pakistani meddling more seriously.
On Monday, US military spokesman Col. James Yonts said foreign militants backed by networks channeling them money and arms had come into Afghanistan to try to subvert the elections.
He said that for "operational security reasons" he could not identify the networks or who was supporting them.
'Al Qaeda regrouping in Afghanistan'
The three men arrested Sunday in the attempted attack on Khalilzad were detained by members of the National Security Directorate, Afghanistan's version of the CIA.
Agents surrounded the men's station wagon when it slowed to go over a speed bump. They found the weapons -- three Kalashnikov assault rifles and an RPG launcher with two shells -- hidden among some clothes.
According to the officials, the suspects told agents they had been trained at a hideout in Wah Cantt, 20 miles west of Islamabad and home to a major Pakistani weapons and munitions factory.
They said they were later moved to a town in the North West Frontier Province called Bara and crossed into Afghanistan last week.
The men allegedly called accomplices in Pakistan and asked that they send suicide vests packed with explosives, but were told they would not arrive in time and were instructed to carry out the assassination with the weapons they had with them.
