Afghan President Hamid Karzai expressed his thanks in a newspaper article Monday for British support in Afghanistan and said the two countries were facing the same "disease" of violent extremism.

Writing in the Times three days after four British troops were killed in southern Afghanistan, Karzai expressed his "profound gratitude" for their presence and sought to highlight the ties between the two countries.

As Prime Minister Gordon Brown -- who was in Kabul at the weekend -- mulls his response to an expected US request to send more troops to Afghanistan next year, the Afghan president urged the British public not to waver.

"I ask for your continuing understanding and support as my country struggles to treat a disease that has infected not just our Afghan lands but... much of the region too: violence fed by uncompromising religious extremism," he wrote.

"An extremism which profanes the religion that I share with two million British Muslims.

"We all need to remember always that the main reason why your brave troops are fighting here, alongside ours, is because that violence also threatens you in the West."

Britain has more than 8,000 troops as part of the NATO-led International Security Assistance Force (ISAF) in Afghanistan.