Britain tells citizens to leave Afghanistan as major city falls to Taliban

Britain has advised its citizens to leave Afghanistan immediately due to the "worsening security situation".

Taliban insurgents seized a provincial capital on Friday amid intensified fighting with government forces across the country.

"All British nationals in Afghanistan are advised to leave now by commercial means," the Foreign, Commonwealth and Development Office said on its website. "If you are still in Afghanistan, you are advised to leave now by commercial means because of the worsening security situation."

The warning came on the same day the Taliban assassinated a senior government spokesman in Kabul and captured their first provincial capital since stepping up attacks across the country in May.

Zaranj, the capital of the south-western province of Nimroz, fell "without a fight", deputy provincial governor Roh Gul Khairzad told AFP.

A spokesperson for the provincial police told Reuters the Taliban had been able to capture the city because of a lack of reinforcements from the government.

The Taliban's nationwide offensive coincides with the withdrawal of US-led foreign forces after nearly two decades of conflict. The insurgents now control vast swathes of rural Afghanistan and are challenging government forces in several cities, including Herat, near the western border with Iran, and Lashkar Gah and Kandahar in the south.

The militants carried out two attacks against officials in the capital past week to pressure the government to stop air strikes on its fighters. Defence Minister Bismillah Mohammadi escaped an assassination attempt in a bomb-and-gun attack on Wednesday, but Dawa Khan Menapal, head of the government's media office, was killed by Taliban gunmen near a mosque in Kabul on Friday.

Taliban attacks on towns and cities are dragging the country into a “deadlier and more destructive” phase of urban warfare, the UN envoy to Afghanistan warned on Friday.

Deborah Lyons told the Security Council that Afghanistan was likely see more of the urban fighting, mass civilian casualties and pitched street battles that were seen during the siege of Sarajevo during the breakup of Yugoslavia in the 1990s and in Syria's towns and cities this past decade.

Russia's UN Ambassador Vassily Nebenzia said the prospects of Afghanistan slipping into full-scale and protracted civil war "is a stark reality".

Britain's ambassador to the UN, Barbara Woodward said the council "should leave the Taliban in no doubt there will be consequences for them if they continue to pursue this military offensive" and pledged that Britain would not recognise a Taliban government that comes to power by force.

Britain's Foreign Office told Britons not to rely on it for emergency evacuation, saying the assistance it could provide was "extremely limited".

"Terrorists are very likely to try to carry out attacks in Afghanistan. Specific methods of attack are evolving and increasing in sophistication," it said.