Jack Straw, appearing at the final public hearing of Britain's inquiry into the Iraq war, told the five-member panel that he discussed with Blair an option for the U.K. to largely withdraw from the initial U.S.-led invasion, but provide military assistance afterward.
"I don't think anybody was keen on military action - it's horrible and people are going to get killed. I was anxious that we should explore all possible alternatives," said Straw, one of a small number of previous witness - including Blair - recalled to provide additional testimony.
Straw said he held a meeting with Blair eight days before the invasion began. He said he "felt that as I owed the prime minister my loyalty, I also owed him the best and most robust advice I could give him."
The veteran minister told the panel, which began hearings in November 2009, he had repeatedly warned Blair that promoting regime change in Iraq could be illegal and had "made that point in quite categorical terms."
Straw, in charge of U.K. foreign policy between 2001 and 2006, said there was "great anxiety" among ministers about President George W. Bush's intentions in the months leading up to the conflict.
But Straw said he had fully endorsed Britain's participation before a vote of Parliament to authorize military action.
The British inquiry was established to make recommendations on how to handle situations like the complex run-up to the war, and the chaotic attempt at nation-building that followed.
The inquiry won't apportion blame, or establish criminal or civil liability, but is expected to produce a report before the end of the year.
Led by John Chilcot, a retired senior government official, the panel has taken public evidence from political leaders, military chiefs and advisers. It also has met with bereaved families, visited the U.S. and France, and held private sessions with intelligence officers.
Chilcot said his team would likely take several months to produce its findings. "We believe it is important that we do justice to all the oral and the huge amount of written evidence we have received," he said.
Last month, the panel released a previously unseen 2002 memo from Blair to his chief of staff, in which the leader called for a "gung-ho" approach toward Saddam Hussein's regime.
However, British authorities refused to allow the inquiry to publish notes - seen by the panel - detailing discussions between Blair and Bush.