KABUL (AFP/Reuters) - NATO forces in Afghanistan killed two civilians on a motorbike after they refused to stop while driving towards a security barrier, the International Security Assistance Force (ISAF) claimed Sunday. The force denied any misconduct in the killings in the southern province of Helmand, saying the pair had refused to listen to warnings and posed a threat. Two Afghan civilians riding a motorcycle were killed after failing to adhere to several warnings to stop while approaching a security perimeter in southern Afghanistan Saturday, the ISAF statement said. The two victims were given several verbal and visual warnings but accelerated towards the barrier, the ISAF said. The two individuals were engaged with lethal force, it said. Initial reports indicate coalition forces followed the appropriate escalation of force procedures. Meanwhile, the alliance said two foreign soldiers battling the Taliban in southern Afghanistan were killed Sunday in a bomb attack. The deaths bring to 536 the number of foreign troops to die in the Afghan war so far this year, compared to 521 for all of 2009, according to an AFP tally based on that kept by icasualties.org. The ISAF said the soldiers died following an improvised explosive device attack in southern Afghanistan, referring to roadside and remote-control bombs laid by the Taliban. The nationalities of the dead were not given, according to policy. Meanwhile, a British woman and three of her Afghan colleagues have been kidnapped by armed men in a remote part of Afghanistan, an Afghan police chief said on Sunday. The police chief for Kunar province said they were seized while visiting an unspecified project in the area. Khalilullah Ziayee described the abductors as armed men, saying a search was launched to find the group. The motive behind the kidnapping was not immediately clear, he said. A spokesman for the Taliban earlier said he was unaware of the incident. In a brief statement Britains Foreign Office confirmed it was urgently investigating reports a British citizen had gone missing in the country.