The assassination of one of the government's leading voices follows another bloody day of fighting in Afghanistan as the war spills into Kabul for the first time in months.

It also comes hours before the UN Security Council meets in New York to discuss the conflict.

"Unfortunately, the savage terrorists have committed a cowardly act once again and martyred a patriotic Afghan," interior ministry spokesman Mirwais Stanikzai said of the death of Dawa Khan Menapal.

Menapal was popular in Kabul's tight-knit media community, and known for pillorying the Taliban on social media -- even jokingly at times.

Former presidential spokesman Sediq Sediqqi said he was "utterly shocked and devastated".

"We lost another great soul," he added.

The Taliban claimed responsibility for the death, with spokesman Zabihullah Mujahid sending a message to media saying "he was killed in a special attack carried out by mujahideen".

The murder comes after the militants warned Wednesday of more attacks targeting Afghan government leaders, a day after the defence minister Bismillah Mohammadi escaped an assassination attempt in a bomb-and-gun attack.

The Afghan and US militaries have stepped up air strikes in their fight against the insurgents in a string of cities, and the Taliban said Tuesday's Kabul raid was their response.

Fighting in Afghanistan's long-running conflict has intensified since May, when foreign forces began the final stage of a withdrawal due to be completed later this month.

The Taliban already control large portions of the countryside, and are now challenging government forces in several provincial capitals.

- 'Nothing left' -

Government forces continue to hit Taliban positions with air strikes and commando raids, and the defence ministry boasted Friday of eliminating more than 400 insurgents in the past 24 hours.

Both sides frequently exaggerate battlefield casualty figures, making independent verification virtually impossible.

But even as Afghan officials claimed to be hitting the Taliban hard, security forces have yet to flush out the militants from provincial capitals they have already entered -- with hundreds of thousands of civilians forced to flee in recent weeks.

Social media is filled with videos of the devastating toll the fighting has taken in the southern city of Lashkar Gah, with posts showing a major market area in flames.

Aid group Action Against Hunger said its offices had been hit by an "aerial bomb" in the city earlier this week, according to a statement released by the organisation on Friday.

"The building was marked from the street and roof as a non-governmental (NGO) organisation, and the office location has been communicated often to the parties involved in the conflict," said the group, adding that no staff had been harmed.

In the western city of Herat, a steady stream of people were leaving their homes in anticipation of a government assault on positions held by the Taliban.

"We completely evacuated," said Ahmad Zia, who lived in the western part of the city.

"We have nothing left and we do not know where to go," he told AFP.