President Obama has praised Britain's "extraordinary" contribution in Afghanistan and extended his sympathy to the families of U.K. troops killed fighting the Taliban.

The president was speaking after the British death toll in Afghanistan rose to 184 following the loss of eight more troops on Thursday and Friday.

"My heart goes out to the families of those British soldiers," Obama said in an exclusive interview with Sky's Political Editor Adam Boulton during his trip to Ghana.

"Great Britain has played an extraordinary role in this coalition, understanding that we cannot allow either Afghanistan or Pakistan to be a safe haven for Al Qaeda."

Obama said it may be necessary for the NATO coalition in Afghanistan to adopt different tactics after the forthcoming elections.

"We knew this summer was going to be tough fighting... we still have a long way to go," he said.

"All of us are going to have to do an evaluation after the Afghan election to see what more we can do.

But he added: "It may not be on the military side, it might be on the development side."

Obama said Britain's contribution to the allied effort in Afghanistan was "critical."

"The likelihood of a terrorist attack in London is just as high if not higher than it is in the U.S., that's the reason why Tony Blair and now Gordon Brown have made this commitment. It is not because they wish to put their young men and women in harm's way."

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