TEHRAN (Reuters) - Iran will prosecute eight British naval personnel seized in its waters, state television said on Tuesday, turning what seemed a minor border incident into a serious diplomatic spat.

The British government immediately demanded an explanation from Tehran of the television report. British officials have had neither access to the men, detained on Monday with their three boats, nor told where they are being held.

Quoting unnamed Iranian military sources, Iran's Arabic language news channel al Alam said the men would be prosecuted on charges of illegally entering Iran's waters.