WASHINGTON - The United States should consider all measures including a no-fly zone in the fight against Islamic State, Gen. John Allen, the outgoing special US.envoy for the coalition against the militant group in Iraq and Syria, told CNN on Thursday."We should consider all the measures," Allen said when asked about a no-fly zone. "We should consider them, whether we would ultimately adopt them or not."He told CNN the goal of such a zone would have to be carefully considered, citing its complexities and costs. President Barack Obama has not supported a no-fly zone in the conflict.