KANDAHAR (AFP) - A British fighter jet crashed in Afghanistan on Monday injuring two pilots, while four US troops were killed in a bomb blast as foreign casualties soar in the war-torn country. The crash and unrelated killing of a British soldier in a bomb attack Sunday bringing to 17 the number killed so far this month was likely to spark renewed political debate in London over Britains role in the conflict. Outgoing NATO chief Jaap de Hoop Scheffer, in London for talks with Prime Minister Gordon Brown, said the recent deaths in Afghanistan were tragic and it was right that there was debate. But he warned: If we were to walk away, Afghanistan would fall to the Taliban, with devastating effect for the people there women in particular. Pakistan would suffer the consequences, with all that implies for international security. Central Asia would see extremism spread. Al-Qaeda would have a free run again and their terrorist ambitions are global. The NATO-led International Security Assistance Force (ISAF) meanwhile said that four soldiers were killed in a bomb blast Monday in the east of the country, a US military spokesman confirming they were from the US. Western military casualties have hit record levels in Afghanistan as foreign governments scramble extra troops to the war-torn nation hoping to ease an increasingly virulent Taliban insurgency ahead of elections on August 20. Mohammad Aslam Yar, a spokesman for the southern Kandahar air base, said an ISAF fighter jet crashed early Monday at the airfield, which is at the biggest military base in the south, a Taliban stronghold. There were two pilots who ejected and were taken to a military hospital inside the base for treatment. Apart from that there are no other casualties. No enemy fire was involved, Yar told AFP. A defence ministry spokeswoman in London told AFP the jet was a Royal Air Force Tornado GR4