A top American diplomat tipped as a possible president of his native Afghanistan has fallen foul of his masters in Washington for fraternising with Benazir Bhutto’s widower, a contender to become president of neighbouring Pakistan.

Zalmay Khalilzad, the US ambassador at the United Nations, has angered senior Bush Administration officials by maintaining what they call “unauthorised contacts” with Asif Ali Zardari, the leader of the Pakistan People’s Party.

The Afghan-born diplomat has reportedly spoken with Mr Zardari several times a week for the past month and planned to meet him privately on Tuesday during a holiday in Dubai.

The New York Times today published a leaked e-mail that Richard Boucher, the Assistant Secretary of State for South Asia, sent Mr Khalilzad after learning of the contacts from Mr Zardari himself.

“Can I ask what sort of ’advice and help’ you are providing?” Mr Boucher asked Mr Khalilzad in the e-mail. ”What sort of channel is this? Governmental, private, personnel?”

Mr Khalilzad, 57, an ethnic Pashtun, was born in the Afghan city of Mazar-e Sharif as the son of a civil servant under the Afghan monarchy. He first came to the United States as a high-school exchange student and eventually earned a PhD in political science at the University of Chicago.

He took up his post as the US representative at the UN after serving as US ambassador first in Afghanistan and then in Iraq, where he was known for reaching out to anti-American factions.

A charming and courteous man, he is well liked at the UN for his back-slapping bonhomie despite the widespread disdain among other delegations for his government’s hawkish policies.

He was recently caught on in-house UN television hugging Libya’s UN ambassador and explained that he was congratulating the Libyan envoy on the marriage of his son.

But he got into trouble with his bosses for sitting next to the Iranian foreign minister at the World Economic Forum in Davos, Switzerland, in January without prior clearance, even though the two countries have no diplomatic ties.

Mr Khalilzad became a friend of Mr Zardari several years ago after meeting him with his wife, Benazir Bhutto, who was assassinated in Pakistan in December.

Richard Grenell, a spokesman for the US mission to the UN, said that he had planned to meet him in his “personal capacity” while on holiday in Dubai but had postponed the meeting after consultations with senior State Department officials.

The friendship between the two men — who could end up as presidents of neighbouring states — has caused a diplomatic headache for the Bush Administration, which is trying to stay out of Pakistan’s internal politics.

“We have maintained a public line that we are not involved in the politics or the details. We are merely keeping in touch with the parties,” Mr Boucher wrote to Mr Khalilzad in his August 18 e-mail. “Can I say that honestly if you’re providing ’advice and help’? Please advise and help me so that I understand what’s going on here.”

Mr Khalilzad, who did not attend a UN Security Council session on Burundi today because he is on holiday, is the focus of continued speculation in Afghanistan that he may return to his native land to run in the presidential election scheduled for next year.

The US ambassador plans to step down in the coming months as the Bush Administration comes to an end, but he has repeatedly said that he will not seek to become Afghan president.

“I am honored to have the opportunity to represent the United States in the United Nations,” he told reporters recently. “This is my job and when I leave this job I will work in the private sector in the United States of America.”

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