A gunman shot dead a Swedish-British journalist at close range in central Kabul on Tuesday in an unexplained daylight murder that shocked foreign residents living in a city on high alert ahead of elections.

Taliban militants denied responsibility for the shooting in an upmarket district of the Afghan capital close to a restaurant where the insurgents killed 21 people, including 13 foreigners, in an attack in January.

Sweden's ambassador to Afghanistan, Peter Semneby, identified the dead man as Nils Horner, 51, a journalist for Swedish national radio.

"He had British nationality in addition to his Swedish nationality. His family has been informed," Semneby told AFP.

Police said the attackers escaped the scene on foot and had not been caught after the assassination-style killing.

A witness described hearing a single gunshot fired before seeing Horner fall to the ground, and a doctor at Kabul's emergency hospital said he was dead on arrival.

"There were two guys who ran away. They were perhaps in their 20s and security guards chased them as they ran away," the witness told AFP on condition of anonymity.

- Experienced reporter -

Security forces cordoned off the street, where blood could be seen on the ground.

Horner, hired by Sveriges Radio in 2001, was an experienced reporter who had been in Afghanistan to witness the fall of the Taliban in 2001 and in Iraq during the war in 2003. He also covered the 2004 Indian Ocean tsunami.

"This is one of the worst days in the history of Sveriges Radio," said station chief Cilla Benko.

"Nils was one of our absolutely best and most experienced correspondents... He was in Kabul three to four times a year. He knew the town and had carried out security checks.

"He was shot in the back of the head in an area not considered to be a risk zone."

According to journalists in Kabul, Hong Kong-based Horner arrived in Afghanistan on Sunday and had planned to stay about a week or 10 days.

"Among Swedish journalists, he was a legend," Johan Nylander, a Swedish freelance journalist based in Hong Kong, told AFP.

"For many years, he didn't even have an apartment. Hong Kong was the first place he put down his suitcase for half a decade."

- City on edge -

The killing comes less than a month before presidential elections in Afghanistan on April 5 and the withdrawal of NATO combat troops by the end of 2014 after 13 years of fighting the Taliban.

On Tuesday, many of the Afghan capital's security forces were on duty at the funeral of Vice-President Marshal Mohammad Qasim Fahim, who died on Sunday.

Horner had recently released a radio piece reporting on Fahim's death, and was researching a story about the restaurant attack in January when he was shot nearby.

The Taliban, who have led the insurgency against the Western-backed government since being toppled from power in 2001, denied any link to the murder.

"We checked with our mujahideen and they are not involved," Taliban spokesman Zabiullah Mujahid told AFP. "We don't take responsibility for this incident."

Foreigners have been targeted before at guesthouses, luxury hotels and embassies in the heavily guarded city, but few have been gunned down in the street.

The Wazir Akbar Khan district is home to several embassies and is one of most highly protected parts of the city.

The attack in January on the Taverna du Liban, a Lebanese restaurant popular with foreigners, was the deadliest on foreign civilians since the Taliban were ousted.

After that attack, security restrictions were tightened for many of the diplomats, aid workers and journalists based in Kabul, where international staff often live and work in fortified compounds.

The next president will face a testing new era as the Afghan army and police attempt to impose security without NATO assistance and as international funding declines.

Among the front-runners in the election are Abdullah Abdullah, who came second in 2009, former foreign minister Zalmai Rassoul and former World Bank economist Ashraf Ghani.