Retired General John Allen, President Barack Obama's special envoy to the coalition fighting Islamic State, said on Thursday the U.S.-led effort is weakening the militant group. "We're clearly degrading its capabilities," Allen told a U.S. House of Representatives Foreign Affairs Committee hearing on Obama's Middle East strategy. Islamic State had lost more than a quarter of the populated territories it had held in Iraq, he said, but added that the situation in Syria is more complex. Several lawmakers questioned Allen closely about U.S. involvement in strikes in the Iraqi city of Tikrit, where Islamic State militants have been holding out for more than three weeks.