REYKJAVIK, Iceland — The United States, which has long provided Iceland with its only military force, has decided to withdraw most of its service members and all of its fighter jets and helicopters from the country later this year, the U.S. ambassador said Thursday. Iceland's government, which had recently offered to pay some of the cost of its defense to try to keep U.S. forces here, said it regretted the decision. In an interview with The Associated Press, U.S. Ambassador Carol van Voorst said she and Nicholas Burns, the U.S. under secretary of state, had told Prime Minister Haldor Asgrimsson...