Image caption Arsala Rahmani was responsible for the committee that looked at freeing Taliban prisoners

A senior Afghan peace negotiator has been shot dead in Kabul, officials say.

Arsala Rahmani was a key member of Afghanistan's High Peace Council, which leads Afghan efforts to make peace with the Taliban.

Correspondents say his death is a major blow to President Hamid Karzai as Mr Rahmani was key in reaching out to Taliban commanders.

It also emerged Afghan forces could soon be in charge of security in areas home to 75% of the population.

Mr Karzai said Afghan National Security Forces will soon take lead responsibility for security in a further 122 areas of the country - a move described as a "significant development" by UK Foreign Secretary William Hague.

It is expected that all of the country will be under the control of Afghan forces by the end of 2014 when NATO's combat mission will end.

Single shot

Police say that Mr Rahmani was shot dead on Sunday morning by an unidentified gunman while on his way to work in western Kabul, in what was described as a carefully planned attack.

Analysis Arsala Rahmani was a unique figure because of his background as a Taliban official who joined peace efforts. He was respected by the Afghan administration as well as by many militant figures. As such, his death is a huge blow to President Karzai's reconciliation efforts. Mr Rahmani really understood how the Taliban leadership operated and the president regularly consulted him on such matters. Observers say he will be extremely difficult to replace as there is nobody of his calibre and experience willing or able to get involved. He was used as an example to other Taliban leaders, who will now be concerned about their safety in Kabul. The Taliban have denied responsibility as they did after the chief of the peace council was killed last year. At that time the finger of blame was pointed at hardline factions within the Taliban and even at elements in Pakistan's security establishment. Pakistan denied any involvement.

Gunmen driving a white Toyota Corolla fired a single bullet using a silencer, the BBC's Bilal Sarwary in Kabul reports.

"Mr Rahmani was shot in his heart and died instantly. His nephew, who was also his driver, didn't even realise he had been shot," Kabul police chief Gen Ayub Salangi told the BBC.

There had been threats against his life in the past and questions will be raised as to why he was travelling without an armed bodyguard, our correspondent says.

Last year the chief of Afghanistan's peace council was killed in a suicide attack.

Burhannudin Rabbani was killed by a bomb hidden in the turban of a suicide attacker posing as a Taliban peace envoy last September.

His US-educated son, Salahuddin Rabbani, was appointed to replace him last month.

The Taliban have denied involvement in the killing of Mr Rahmani.

An Isaf statement condemned the killing and paid tribute to Mr Rahmani: "His decision to help make the future brighter for Afghans serves as an inspiration to us all and his contributions will be missed".

Mr Rahmani was one of the first senior Taliban members to join the peace process and his death will be of concern to other Taliban officials considering engaging with the government, a senior presidential aide told our correspondent.

He was a critical figure in President Karzai's plans to reach out to Taliban commanders, although it is unclear how many senior leaders he managed to bring into the fold.

Nevertheless the president frequently consulted him to gain insight into the inner workings and the thinking of the Taliban leadership.

Mr Rahmani was responsible for the committee within the peace council that considers the release of Taliban prisoners from Bagram and other Afghan prisons.

Arsala Rahmani biography Appointed as senior member of Afghanistan's High Peace Council, after it was set up in 2010

As a former education minister for the Taliban, he was seen as crucial in efforts to reach out to militants

Close to President Karzai who frequently consulted him to gain insight to Taliban thinking

The UN removed his name from a sanctions blacklist - a signal of support to reconciliation efforts

He was politically active well before the birth of the Taliban movement, holding political office in various administrations during the 1990s

Most recently he was responsible for the committee that looked at the fate of Taliban fighters in Bagram and other Afghan prisons

He served as minister of higher education in the Taliban administration that ruled Afghanistan for five years until the US drove them from power in 2001.

But he had been politically active long before the birth of the Taliban movement, holding political office in Afghan administrations during the 1990s.

And he was one of several former Taliban officials removed from a UN blacklist last July as a signal of support for Afghan peace efforts, which meant that a travel ban and assets freeze were lifted.

Afghanistan's 70-member peace council was set up two years ago by President Karzai to open negotiations with insurgents.

The council was credited with reconciling hundreds of Taliban field commanders, but had failed to woo any senior figures away from the insurgency.

Although the Taliban denied sanctioning last year's killing of Mr Rabbani, they view the Western-backed Karzai government as illegitimate.

And in March the militants suspended parallel preliminary peace negotiations with the United States, saying US efforts to involve the Afghan authorities were a key stumbling block.