our diplomatic correspondent paul adams reports. the american say the attack happened at abase known as tower 22, right on the syrian jordanian border. it is one of many american bases across the region. there have been dozens of drone and missile attacks in recent months, but no american personnel had been killed until now. joe biden, seen here attending church this morning, was quick to point the finger. we know it was carried out by radical iran backed militant groups operating in syria and iraq, he said. it s not necessarily a tipping point into uncontrolled escalation between the united states and iran, but is a dangerous step because, as i say, the us will have to respond even more strongly than it has done to previous attacks. carefully cultivated over yea rs, iran has a wide network of allies and proxies operating in countries across the middle east. they are all opposed to israel and the united states it s sometimes called the axis of resistance. there are pro ir