New Delhi, Aug 13 (IANS): The Taliban on Friday captured Kandahar, Afghanistan's second largest city, delivering a crushing blow for the government in Kabul and a major win for the militants.

The city was once the Taliban's stronghold, and is strategically important as a leading trade hub, the BBC reported. Kandahar is the latest provincial capital to fall, after Herat and Ghazni on Thursday.

Meanwhile, the US said it is sending nearly 3,000 troops back into Afghanistan to help evacuate staff from the American embassy.

The US said it was sending troops to the airport in Kabul to help evacuate a "significant" number of embassy staff on special flights.

The UK said it was also deploying about 600 troops on a short-term basis to provide support to British nationals leaving the country.

The insurgents have moved quickly, seizing new territories as the US and other foreign troops withdraw after 20 years of military operations.

Within hours of each other on Thursday some of Afghanistan's most important cities were captured - Herat, Ghazni and Qala-I-Naw came under Taliban control.

A Taliban spokesman also announced that "Kandahar is completely conquered".

Sources have told the BBC that the southern city of Lashkar Gah, the capital of Helmand province, has also been taken by the militants, although this has also not been confirmed.

The Taliban now control most of northern Afghanistan and about a third of the country's regional capitals.

There are increasing concerns that the militants will continue their lightning speed offensive toward the capital, Kabul, where tens of thousands of civilians have fled violent street fighting.

Kandahar is the Taliban's birthplace and former stronghold, taking control of the city would be a significant prize for the militants.

They had occupied the city's outskirts for a number of weeks before launching their attack on the centre.

The report said that on Wednesday, the Taliban breached Kandahar's central prison, and on Thursday, images on social media reportedly showed insurgents in the city centre.

Kandahar is considered strategically important because of its international airport, its agricultural and industrial output and its position as one of the country's main trading hubs.

Ghazni, captured on Thursday, is a significant gain for the Taliban as it is on the Kabul-Kandahar motorway, linking militant strongholds in the south to the national capital.

Meanwhile Herat, an ancient silk road city, had been under siege for weeks before security forces retreated to army barracks.

Video on social media shows the insurgents running through a central street firing their weapons, and the Taliban flag was seen flying over the police headquarters.