Iraq has quietly started negotiations to buy U.S. fighter jets and air-defense systems worth billions of dollars, a purchase Washington hopes will help counter Iranian influences and cement long-term ties with Baghdad after American troops pull out. Baghdad had frozen plans to buy 18 advanced U.S. F-16 fighters earlier this year after the Arab Spring protests in the region turned its attention to internal stability. Now, senior U.S. and Iraqi officials said Iraq is considering raising its purchase to as many as 36 of the jets. The decision by Iraqi Prime Minister Nouri al-Maliki to renew the F-16 talks follows an unexpected surge in government oil revenue, and comes as a Dec. 31 deadline approaches for the departure of the 46,000 remaining U.S. troops from Iraq.