KABUL: The Afghan army was planning a major counter-attack Wednesday to drive the Taliban out of a key southern city, warning residents they must immediately flee their homes.

Dozens of civilians have already died in the battle for Lashkar Gah, a city of 200,000 people that would be the Taliban's biggest urban prize since the insurgents launched a nationwide offensive in May.

The Taliban have taken control of vast swathes of the countryside and key border towns as they have rushed to fill the vacuum left by withdrawing US forces.

More than 1,000 Afghan troops flee into Tajikistan

They are now targeting the urban centres, with fierce fighting since last week in the cities of Herat near the western border with Iran, and Kandahar in the south, as well as Lashkar Gah.

There was also violence in Kabul on Tuesday night, with coordinated bomb and gun attacks targeting Defence Minister Bismillah Mohammadi and other politicians that claimed at least four lives.

Authorities said the attackers had been repelled, and that Mohammadi was safe.

But the violence again highlighted the imminent threats facing the government as it seeks to hold on to power.

'Forgive us'

The loss of Lashkar Gah, the capital of southern Helmand province, would be a massive strategic and psychological blow for the government.

With the Taliban having taken control of some radio and TV stations in the city, and moved into people's homes, the Afghan army on Tuesday flagged a major counter-offensive.

"Please leave as soon as possible so that we can start our operation," General Sami Sadat, commander of the 215 Maiwand Afghan Army Corps, said in a message to the city's population.

"I know it is very difficult for you to leave your houses -- it is hard for us too -- but if you are displaced for a few days, please forgive us.

"We are fighting the Taliban wherever they are."

Sefatullah, director of Sukon radio in Lashkar Gah described the fighting on Tuesday as intense.

He said US and Afghan air force planes had pounded Taliban positions, and that fighting was ongoing near the city's prison and a compound housing the headquarters of the police and intelligence agencies.

One resident provided a harrowing account to AFP on Tuesday for people unable to leave Lashkar Gah.

The United Nation reported Tuesday that at least 40 civilians had been killed in Lashkar Gah in the previous 24 hours.

Taliban 'hallmarks'

In Kabul, the first bomb blew up in the centre of the city late on Tuesday, sending a thick plume of smoke into the sky, AFP correspondents reported.

Mohammadi said it was a suicide car bomb attack targeting his house.

Less than two hours after the car bomb detonated, another loud blast followed by smaller explosions and rapid gunfire again shook Kabul, also near the high-security Green Zone that houses several embassies, including the US mission.

A security source said several attackers had stormed a lawmaker's house after setting off the car bomb and shot at the residence of the defence minister from there.

"Several lawmakers were meeting at the house of this MP to make a plan to counter the Taliban offensive in the north," the source told AFP.

No group has yet claimed the attack, but Washington pointed the finger at the Taliban.

"We're not in a position to attribute it officially just yet but of course it does bear all the hallmarks of the spate of Taliban attacks that we have seen in recent weeks," State Department spokesman Ned Price told reporters.

"We unequivocally condemn the bombing, and we continue to stand by our (Afghan) partners."