AFP, Kandahar :At least 20 Afghan policemen were killed on Tuesday in a Taliban attack near Kabul, bringing to 26 the number of officers to die since the start of an army offensive aimed at weakening the insurgents.The assault saw Taliban gunmen and suicide attackers strike police headquarters in Puli Alam city, south of Kabul. Provincial police chief Abdul Hakim Ishaqzai told AFP that in addition to those killed, nine were wounded.The attack came as police and troops, in their first major assault since US-led Nato forces ended their combat mission last December, began targeting militants on Monday in restive Helmand province, a hotbed of the Taliban insurgency and a hub for drug trafficking.The defence ministry said 76 insurgents were killed on Monday, the first day of the operation, which will also target militants in six districts in neighbouring Kandahar, Farah, and Uruzgan provinces. The offensive is designed to hurt the Taliban before the start of the so-called “fighting season”.”This is a totally Afghan-planned and Afghan-led operation. It will continue until success is achieved,” said General Abdul Khaliq, who commands the operation.The Taliban’s spokesman was not immediately available for comment.The defence ministry said the assault, code-named “Zolfiqar”, was the first in a planned series of large-scale operations by Afghan forces after Nato ended its combat mission in December.”This is not the first and will be not be the last operation against the Taliban and their allies,” said ministry spokesman General Dawlat Waziri.Experts and Afghan military officials anticipate a surge in Taliban violence with the start of the traditional spring and summer fighting season in April or May. Some observers have warned that unusually early warm weather this year may have already encouraged militants to venture out of their hideouts in the rugged mountainous area along the border with Pakistan.Highlighting the dangers to Afghan forces, at least 20 policemen were killed in Tuesday’s attack in Puli Alam. Niaz Mohammad Amiri, acting governor of Logar province where the attack took place, confirmed the provincial police chief’s toll.Meanwhile, the number of civilian deaths and injuries in Afghanistan rose by 22% in 2014, the United Nations says.A total of 3,699 Afghans killed and 6,849 injured made 2014 the deadliest year since the UN began keeping records in 2009.For the first time more people were killed in battles between the Taliban and government forces than by roadside bombs, the figures show.Foreign troops formally ended their combat role last December.Fighting between government forces and the Taliban accounted for just over a third of civilian casualties, while roadside bombs were responsible for 28% of civilian deaths and injuries, UN Special Representative Nicholas Haysom said, presenting the latest figures in Kabul.Intensified ground fighting is also reflected in the latest figures published by the International Committee of the Red Cross (ICRC).