BRUSSELS (Reuters) - NATO warned on Monday that an early presidential election in Afghanistan would have implications for security and said it would be better able to protect the poll if it were held in August.

Afghan President Hamid Karzai said on Saturday the vote should be held by May, putting him on a collision course with the country's election commission which set an August 20 date and with Washington and its NATO allies, who have pledged military reinforcements to protect the process.

NATO spokesman James Appathurai said when the election was held was an Afghan decision, but added: The bottom line is that we will be able to provide more support and more security for an August election than we would for an earlier one.

(Reporting by David Brunnstrom; Editing by Janet Lawrence)