British Prime Minister Gordon Brown will use a speech Monday to defend the unpopular war in Afghanistan, arguing that the campaign is preventing Al Qaeda from making the country a safe haven.

Brown's office said the prime minister would use his annual foreign policy address at the Lord Mayor's Banquet in London to say that "more has been planned and enacted with greater success in this one year to disable Al Qaeda than in any year since the original invasion in 2001."

Excerpts from the speech were released in advance.

Brown will say that Al Qaeda — driven from Afghanistan to Pakistan after the fall of the Taliban — could return if international forces leave.

"We are in Afghanistan because we judge that if the Taliban regained power, Al Qaeda and other terrorist groups would once more have an environment in which they could operate," he plans to say.

"So I vigorously defend our action in Afghanistan and Pakistan because Al Qaeda is today the biggest source of threat to our national security — and to the security of people's lives in Britain," Brown will add.

Britain has 9,000 troops in Afghanistan, the largest international contingent in Afghanistan after the United States. Brown has offered unwavering support to President Barack Obama as the U.S. leader considers sending as many as 40,000 more soldiers to the country.

Monday's speech comes amid rising casualties and falling support in Britain for the war.

On Sunday a British soldier was shot dead in southern Afghanistan, taking Britain's death toll there to 233 since the start of operations in 2001.

Some 71 percent of respondents to a poll for the Independent on Sunday newspaper said they supported a phased withdrawal leading to an end of combat operations within a year. Only 22 percent disagreed.

The survey also showed skepticism about the government's claim that the war is vital to protecting Britain from Al Qaeda terrorism. Forty-seven percent of those polled said they thought Britain's involvement made terrorism at home more likely, while 44 percent disagreed.

Pollster ComRes interviewed 1,007 adults by telephone on Wednesday and Thursday. The poll's margin of error is plus or minus three percentage points.