London - Britain's special representative to Afghanistan and Pakistan is quitting with immediate effect, London said Wednesday, following a reported clash with NATO and US officials on fighting the Taliban.

Sherard Cowper-Coles temporarily stepped down in June but the Foreign Office had said he would return later this year.

Foreign Secretary William Hague said in a statement released by the Foreign Office: "Sherard has made an invaluable contribution to UK policy towards Afghanistan and Pakistan."

Hague added that Karen Pierce, the Foreign Office's South Asia and Afghanistan director, would be taking over as special representative.

The Guardian newspaper reported in June that there were serious disagreements in recent months between Cowper-Coles and officials from military alliance NATO, which is leading international troops in the country, and the United States.