British Prime Minister Gordon Brown warned Friday that continued support for Afghanistan hinges on the government of that country moving to clean up corruption.

"I am not prepared to put the lives of British men and women in harm's way for a government that does not stand up against corruption," Brown said in speech at the Royal College of Defence Studies in London.

The statement by Brown is viewed as an early challenge to Afghan President Hamid Karzai, who was recently declared re-elected after his competitor dropped out of an election run-off.

Brown's comments also come as he faces increased pressure at home over his country's involvement in Afghanistan. The British military suffered seven deaths in the country this week, including five shot dead by an Afghan police officer.

While he urged the Afghan government to get tough on corruption, Brown said U.K. military action there is key to British home security.

"We will not be deterred, dissuaded or diverted from taking whatever measures are necessary to protect our security," Brown said.

A spokesman for Karzai said Afghanistan and other countries must work together to counter corruption.

"The president has renewed his commitment in fighting this menace by redoubling his government's efforts," Humayun Hamidzada said. "But fighting corruption requires closer and more effective co-operation between the government of Afghanistan and the international community."

Eyes are still on the direction that the United States will choose in Afghanistan. President Barack Obama is mulling whether to increase U.S. troop strength in Afghanistan by 40,000 — as recommended by his top general there — or choose another course or action.

A top NATO leader warned that waning public support could undermine military efforts in Afghanistan.

"The clock in Afghanistan is clearly running against us," said German Gen. Egon Ramms, whose Allied Joint Forces Command oversees NATO forces in Afghanistan.

"In the end, politicians will not go against their public opinion," said Ramms.

In March 2008, Parliament voted to extend the Canadian mission in Afghanistan until July 2011. The parliamentary motion said all troops must be out of Afghanistan by the end of that year.

There are 2,800 Canadian soldiers in Afghanistan, based primarily in Kandahar province.

CBC News reported Friday that the head of the Canadian Armed Forces has issued orders to prepare to withdraw from Afghanistan in 2011 in the absence of a clear direction from government on the mission's future shape.

Chief of the Defence Staff Gen. Walt Natynczyk has ordered his commanders to start preparing military plans to pull out of Afghanistan and return thousands of soldiers and billions of dollars' worth of equipment to Canada.