In a move to bolster military strength against Iran, 20 nations will stage an anti-mining exercise in Mideast waterways.

Defense Department press Secretary George Little said the large minesweeping exercise Sept. 16-27 is a defensive drill and is "not ... aimed to deliver a message to Iran."

But Iran has threatened to close the Strait of Hormuz, the route for one-fifth of the world's oil, in retaliation for international sanctions over Tehran's nuclear program.

The upcoming exercise will focus on "a hypothetical threat from an extremist organization to mine the international strategic waterways of the Middle East, including the Red Sea, the Gulf of Aden, the Gulf of Oman, and the Persian Gulf, although exercise activities will not extend into the Strait of Hormuz," U.S. Central Command said in a statement.

"This is a defensive exercise aimed at preserving freedom of navigation in the international waterways of the Middle East and aimed at promoting regional stability," Little told Pentagon reporters on Tuesday.