Jeremy Greenstock, former U.K. ambassador to the United Nations, arrives at the Iraq inquiry in London Friday. Greenstock said the U.S. undermined the efforts of British diplomats to gain UN approval for military action in Iraq. (Kirsty Wigglesworth/Associated Press)

The 2003 military invasion of Iraq was legal but of "questionable legitimacy" because it lacked international backing, Britain's former ambassador to the United Nations told an inquiry Friday.

Jeremy Greenstock testified before an inquiry in London examining Britain's role in the Iraq war that U.K. diplomats had tried to get a UN resolution sanctioning the military action prior to the invasion but the United States undermined their efforts.

"The United States was not proactively supportive of the U.K.'s efforts and seemed to be preparing for conflict whatever the U.K. decided to do," Greenstock wrote in a written statement to the inquiry.

He said the U.S. stance was "decidedly unhelpful to what I was trying to do in New York."

The UN passed a resolution in November 2002 that paved the way for inspectors to return to Iraq to verify that it was not developing nuclear weapons. However, Britain and the U.S. were unable to get a second resolution passed in March 2003 to directly authorize the use of military force in Iraq if then leader Saddam Hussein refused to let inspectors into the country. The invasion began days later.

“I regarded our invasion of Iraq as legal but of questionable legitimacy in that it didn’t have the democratically observable backing of the great majority of member states or even, perhaps, of a majority of people inside the U.K.," Greenstock told the inquiry.

Probe focusing on lead-up to war

The inquiry, which began on Tuesday, is looking into whether former U.K. prime minister Tony Blair pledged support for the invasion of Iraq before the U.K. parliament approved military involvement in 2003.

The panel hearing testimony at the inquiry won't lay blame or establish criminal or civil liability but will give reprimands if warranted and make recommendations.

Greenstock, who served as Britain's envoy in Iraq after the invasion, told the inquiry that serious preparations for war had begun in early 2002.

He concurred with Christopher Meyer, Britain's former ambassador to the U.S., who told the inquiry on Thursday he believed then U.S. president George W. Bush and Blair had made an agreement to take military action during a meeting at Bush's ranch in Crawford, Texas, in April 2002.

Greenstock said that following that meeting, Britain "was being drawn into quite a different discussion."

But, like Meyer, he said the talks were secretive and were not disclosed to diplomats.

"That discussion was not totally visible to me," Greenstock said. "I was not being politically naive, but I was not being politically informed either."

The British military formally ended six years of combat operations in Iraq on April 30, 2009, handing over control of its main base in Basra to a U.S. brigade.

A total of 179 British soldiers lost their lives during the U.K. involvement in Iraq.

With files from The Associated Press