KABUL (Agencies) A string of bomb, rocket and gun attacks across southern Afghanistan have killed 12 NATO troops in just two days, officials said Wednesday, throwing the spotlight on the spiralling cost of the war. The brazen assaults followed the killing of three British troops by a rogue Afghan soldier, an incident that has underscored concerns over efforts to build up the local army, a cornerstone of the US-led war strategy. Another British soldier died from wounds in another incident. Among the 12 dead, four were British troops and eight American. Four American soldiers were killed in a Taliban-style bombing and a fifth US service member by small-arms fire in the volatile south on Wednesday, NATOs International Security Assistance Force (ISAF) said. Late Tuesday, a suicide attacker slammed the car bomb into the gate of the headquarters of the elite Afghan National Civil Order Police in Kandahar, a NATO statement said. Minutes later, insurgents opened fire with machine guns and rocket-propelled grenades. Three US troops, an Afghan policeman and five civilians died in the attack, but NATO said the insurgents failed to enter the compound. The special police unit, known as ANCOP, had only recently been dispatched to Kandahar to set up checkpoints along with international forces to try to secure the souths largest city, the spiritual birthplace of the Taliban. Zalmai Ayoubi, a spokesman for the Kandahar government, told AFP the car bomb was set off by a suicide bomber, adding that several other insurgents attacked the base with rockets and machine-gun fire for more than 20 minutes. The interior ministry said another nine civilians were killed in the neighbouring province of Helmand on Tuesday when the minivan they were travelling in hit a roadside bomb - the Talibans weapon of choice. A similar bomb killed two private security guards in Paktia province on the eastern border with Pakistan, it added. The violence flared on the heels of the killing Tuesday by a renegade soldier of three members of a British Gurkha battalion on a base in Helmand, one of the most violent parts of the country. At least 365 NATO soldiers have died in the conflict so far this year, compared with 521 for all of 2009.