The UK's most senior diplomat in Afghanistan, special envoy Sir Sherard Cowper-Coles, is leaving his post.
He will take leave over an extended summer break, the Foreign Office said. It is not clear to what role he will return in the autumn.
Sir Sherard is on leave while the foreign secretary reviews the post, a Foreign Office source told the BBC.
The diplomat has been critical of Nato and US policy, and said talks with the Taliban should have greater priority.
'Completed his job'
Sir Sherard has worked on Afghanistan and Pakistan for more than three years.
He was appointed special envoy in February 2009 after serving as ambassador to Kabul.
The BBC understands that he was not sacked, as has been reported in some newspapers.
But Sir Sherard is said to feel he has completed his job and successfully put across the message that the political process in Afghanistan needs to be more inclusive.
He has advocated that the Taliban and other insurgent groups in Afghanistan need to be included in discussions about the future direction of the country.
But he is reported to have clashed with senior Nato and US officials over his approach.
It is understood he had asked to be released so he could apply for other positions in the Foreign Office.
A Foreign Office source told the BBC the foreign secretary, William Hague, would review the post of special envoy to Afghanistan and how the Afghan dossier was handled.
It also said Mr Hague had wanted Sir Sherard to remain in his position.
News of the diplomat's departure came on Monday as the Ministry of Defence confirmed the 300th British fatality in Afghanistan since operations began in 2001.
The man, from 40 Commando Royal Marines, died in Birmingham's New Queen Elizabeth Hospital on Sunday after being injured in a blast in the Sangin district of Helmand on 12 June.
And it comes ahead of important international talks next month in Kabul, hosted by President Hamid Karzai and United Nations Secretary General Ban Ki-moon.
Karen Pierce, Foreign Office director for Afghanistan and South Asia, will take over as acting special representative.