Khalilzad said he was also referring to Saudi Arabia when he wrote in an opinion piece in the New York Times last week that "several of Iraq's neighbours - not only Syria and Iran but also some friends of the US - are pursuing destabilising policies".
"Yes, well, there is no question that ... Saudi Arabia and a number of other countries are not doing all they can to help us in Iraq," Khalilzad, the former US ambassador to Iraq, said.
The envoy said that some of Iraq's neighbours were not engaging the government or the Shia-led majority and had no diplomatic representation in Baghdad.
"The level of positive effort that they are making compared to the stakes involved for the region is minimal," he said.
Iraqi officials have openly accused Saudi Arabia of funding Sunni fighters and failing to prevent would-be suicide bombers from crossing the Saudi border into Iraq.
Khalilzad's comments came a day before Condoleezza Rice, the US secretary of state, and Robert Gates, US defence secretary, go to the Middle East to bolster Iraq and discuss weapons sales with allies.
Rice and Gates will make rare joint visits to Egypt and Saudi Arabia before separate trips to other parts of the region.
|Rice will also travel to Jerusalem and Ramallah to meet Israeli and Palestinian officials [AFP]|
The duo "are going to be talking to the Saudis as well as others about what they might do" in supporting the Iraqi government, not only on the security front but also diplomatically and financially, Sean McCormack, the US state department spokesman, said.
In a bid to soothe concerns of pro-Western Sunni nations worried about Iran, Washington is also expected to discuss military aid packages and arms sales with them.
The arms deals, according to one administration official, are aimed at shoring up US allies in the Middle East and countering "a more aggressive Iran".
US allies in the Gulf are "very concerned about what our commitment and the possibility of withdrawal from Iraq means for the region", a Pentagon official said.
Arms deal block
In related news, Anthony Weiner and Jerrold Nadler, two US Democratic representatives, said on Sunday, they would introduce legislation to block the Saudi arms deal, accusing the oil-rich country of exporting terrorism and acting against US interests.
"We need to send a crystal clear message to the Saudi Arabian government that their tacit approval of terrorism can't go unpunished," Weiner said.
"Saudi Arabia should not get an ounce of military support from the US until they unequivocally denounce terrorism and take tangible steps to prevent it."
Weiner and Nadler said they would introduce legislation to block the deal, and emphasised that 15 of the 19 hijackers on September 11, 2001, were Saudi citizens.
US media has reported that the Bush administration is set to announce a series of arms deals worth at least $20bn with Saudi Arabia and the five other Gulf states on Monday.