WASHINGTON (AFP) – A top aide to Abu Musab al-Zarqawi, head of the Al-Qaeda operation in Iraq and accused of masterminding high-profile suicide bombings in the country, has been killed by Iraqi security forces, defense officials have confirmed.

But the battlefield success hardly impressed two leading US senators, who on Sunday questioned the Pentagon”s handling of the situation in Iraq and said they no longer had confidence in Defense Secretary Donald Rumsfeld.

Abu Zubair, also known as Mohammed Salah Sultan, was gunned down in the northern city of Mosul Friday, when he got caught in an ambush set up by Iraqi security forces, the officials said, confirming a report by Mosul police.

No other details of the operation were provided. But officials pointed out Abu Zubair was wearing a suicide belt filled with metal pellets when he was killed.

It was not immediately clear whether the suspect intended to become a suicide bomber himself or the belt was to be used by somebody else.

Abu Zubair was wanted for his alleged role in, among other things, organizing a bombing attack on an Iraqi police station in Mosul last month, in which five policemen were killed, according to the defense officials.

They noted that Abu Zubair”s death followed the capture of three bombmakers and six foreign fighters by US and Iraqi security forces last week.

&#34Abu Zubair”s death, as well as recent captures of terrorists in northern Iraq, is making a difference in coalition and Iraqi security forces efforts to disrupt terrorists operating in this part of the country,&#34 Colonel Bill Buckner, a spokesman for the multinational force, told reporters.

He expressed confidence that bombings and other insurgent attacks &#34will not prevent Iraqi democracy.&#34

But Joseph Biden, the top Democrat on the US Senate Foreign Relations Committee, said that judging by the way things were unfolding in Iraq, democracy there &#34will not happen in my lifetime.&#34

He argued the most the Bush administration could hope for under the circumstances was a government that would be able to secure public safety and not be a threat to its neighbors.

Criticism of the administration”s Iraq policy grew louder this month as the US casualty toll spiked, raising the possibility August will become one of the deadliest for Americans since the beginning of the year.

At least 44 US military personnel have been killed in Iraq since the first of the month, despite a steady drumbeat of official assurances the administration of President George W. Bush was making progress in the country.

&#34I think Rumsfeld should get his notice on Monday morning,&#34 Biden said as he appeared on NBC”s &#34Meet the Press&#34 program.

Republican Senator John McCain, a possible presidential candidate in 2008, echoed the view, adding, &#34I don”t have confidence&#34 in Rumsfeld.

McCain was particularly incensed by recent statements by General George Casey, the top US military commander in Iraq, and other Pentagon officials that substantial withdrawals from Iraq could begin as early as next year.

&#34Look, I”ve got an idea for our Pentagon planners,&#34 the Arizona senator opined testily on the Fox News Sunday show. &#34The day that I can land at the airport in Baghdad and ride in an unarmed car down the highway to the ”green zone” is the day that I”ll start considering withdrawals from Iraq.&#34

Biden, for his part, accused the defense secretary of being personally responsible for the US failure to get broader support for the US-led operation in Iraq from NATO allies.

&#34As long as Rumsfeld”s in charge of this operation, as opposed to the uniformed military, they virtually have no confidence in our ability to get the job done,&#34 the Delaware Democrat pointed out.