KABUL (AFP) - Four US soldiers were killed Sunday while fighting the Taliban in Afghanistan, NATO said, as the insurgents appeared to step up their campaign against officials and election candidates. The four American troopers died in three separate incidents, in eastern and southern Afghanistan, NATOs International Security Assistance Force (ISAF) said. ISAF spokesman US Air Force Master Sergeant Jason Haag confirmed all four were Americans. The deaths bring to 451 the total number of international soldiers to die in the Afghan war so far this year, according to an AFP tally based on that kept by the icasualties.org website. The total in 2009 was 520. Two of the soldiers were killed in the same incident in eastern Afghanistan, while the other two died in separate incidents in the south - one in an insurgent attack, the other after an attack with a makeshift bomb, ISAF said. There are close to 150,000 troops in Afghanistan in a US-led NATO force fighting to shore up Afghanistans government and fight a Taliban-led insurgency, raging since the Islamists were thrown from power in late 2001. As the country prepares to hold its second parliamentary elections next month, the insurgents appear to be acting on pledges to target candidates, as well as anyone associated with the govt or foreign forces. The brother of a candidate running for parliament in the western province of Herat was killed on Saturday in a Taliban attack on a crowd who had gathered to hear a campaign speech. Abdul Hadi Jamshidi, the candidate, said: I was speaking to a public gathering as part of my election campaign in Kushk Robat Sangi district when terrorists opened fire, killing my brother and wounding three of my guards. Herat police spokesman Abdul Rauof Ahmadi confirmed the incident. Officials in the southern insurgency hotspot of Kandahar said the second-in-command of security for the inter-provincial Kandahar-Uruzgan highway was shot dead early Sunday by unidentified gunmen. At around 9:00am (0430 GMT) unknown armed motorcyclists opened fire on the vehicle of Haji Abdul Wahid. He died on the spot, said Kandahar deputy police chief Mohammad Shah Farooqi, adding that the attackers escaped. Elsewhere in Kandahar, according to officials, at least nine insurgents including a commander were killed in a joint operation between NATO and Afghan security forces. Five other Taliban were wounded in the 24-hour operation, the Kandahar governors spokesman Zalmai Ayobi said.