The top U.S. and NATO commander in Afghanistan says success there will take time, patience and resolve.

But Gen. Stanley McChrystal acknowledged Thursday that NATO does not have an indefinite amount of time to defeat the Taliban insurgency.

McChrystal told reporters and academics at the London think-tank, the International Institute for Strategic Studies, that success will depend on convincing ordinary Afghans that coalition forces could help deliver a better life.

The general says public support will not last indefinitely — and that some things are going to have to be done dramatically differently.

McChrystal is believed to be seeking up to 40,000 more U.S. troops to fight the Taliban-led insurgency and help Afghanistan rebuild.