The Taliban offensive in Afghanistan is "gradually running out of steam" as the group lacks resources to take over major cities, Interfax news agency quoted a senior official at Russia's foreign ministry as saying on Thursday.

Alexander Vikantov, deputy head of information and press at the ministry, cited examples where Afghan government forces were able to retake some districts captured by the Taliban last month, although he added that insurgent activity was notable this month near big provincial centres.

"The Taliban lack the resources to take over and hold major cities including the capital, Kabul. Their offensive is gradually running out of steam," he said.

Russia would continue to press for peace talks, he added.

The Taliban's rapid territorial gains in Afghanistan's rural areas over the last few months caught many off guard, particularly the Afghan government.

While the pace of that blitz has slowed, insurgent fighters have turned their attention to urban centres, penetrating deep into three key provincial capitals, which many fear could fall into Taliban control.

Fighting has been particularly heavy inside the city of Herat, near the western border with Iran, Lashkar Gah, capital of Helmand province in the southwest, and Kandahar in the south.

Three Taliban commanders told Reuters they had switched strategy from targeting rural areas to attacking provincial cities, in response to increased U.S. air strikes after the United States said it was ending its longest war.

An Afghan military spokesman said this week an emergency had been declared in Lashkar Gah and government forces were getting reinforcements and U.S. air support. "Special forces have been sent to the area. They are in good morale," armed forces spokesman General Ajmal Omar Shinwari told Reuters.

The loss of Lashkar Gah would be a huge blow for the government, which has pledged to defend strategic centres after losing many rural districts to the Taliban in recent months.