KABUL: 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.

Four soldiers were killed in a Taliban-style bombing and a fifth by small-arms fire in the volatile south on Wednesday, NATO`s International Security Assistance Force (ISAF) said.

Late Tuesday, Taliban insurgents had set off a car bomb, then fired rockets and small arms into a police base in the southern province of Kandahar, killing three US soldiers and five Afghan civilians.

Afghan police backed by international forces fought back "and prevented insurgents from penetrating the compound perimeter," ISAF said.

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 Taliban`s 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.

President Hamid Karzai and the Afghan army chief have vowed a full investigation into the shooting.

Britain, the main US ally in the war against the Taliban, said it would not alter its strategy in working with local forces, which is key in enabling them to take over security and allow for an eventual exit for US-led troops.

US General David Petraeus, who assumed command of NATO troops this month, said it was vital to ensure that the trust between Afghan and international forces "remains solid in order to defeat our common enemies".

Officials of NATO`s Training Mission-Afghanistan -- costing more than 10 billion dollars, mostly from US coffers -- say they aimed to recruit and train 171,000 soldiers and 134,000 police officers.

Current figures are around 115,000 in the army and 104,000 in the police. Illiteracy, desertion and drug addiction are widespread problems.

"It`s a game of patience," a Western military official told AFP.

Afghanistan`s ability to take over responsibility for securing its borders and quelling insurgency is seen as vital to Western plans to end engagement in a war NATO and its allies have been fighting since 2001.

"There is no alternative to training a strong Afghan army and security force which can replace foreign troops in the long run," said political analyst Mohammad Younus Fakur.

"The enemy will try to use this (attacks on Western military) as a permanent tactic to create mistrust among forces who fight alongside each other, and that could be disastrous for the friendly forces."

There have been fears that as the war loses ground with the Western public, pressure to reach quotas will override quality.

Britain has around 10,000 soldiers in Afghanistan and British Prime Minister David Cameron has signalled he would like to see combat troops withdraw within five years. A British marine was shot dead on Tuesday while on foot patrol.

The United States and NATO have 143,000 troops in Afghanistan, with the number due to rise to 150,000 in coming weeks as international forces step up their campaign against the Taliban.

Military officials said the three dead soldiers were from a Gurkha battalion, whose troops are drawn from Nepal, but have not given details on their nationalities. Several more were also wounded in the attack.

BDST: 1802 HRS, July 14, 2010