Four times as many U.S. troops as originally planned are to take part in a joint military exercise with South Korea next month following nuclear and missile tests by the North, Seoul said Thursday, February 18, AFP reports.

The U.S. will send 15,000 troops to the annual computer-simulated "Key Resolve" exercise, the Yonhap news agency quoted Defense Minister Han Min-Goo as saying, up from 3,700 last year.

South Korea would also increase the number of troops it sends, he said.

Key Resolve, which ran for 10 days last year, usually kicks off simultaneously with a field exercise known as Foal Eagle, another joint military drill that lasts around 50 days.

Foal Eagle is also expected to be the largest ever this year, attracting key U.S. strategic assets such as an airforce combat brigade, marines, a naval fleet led by an aircraft carrier and nuclear-powered submarines, Yonhap said.

North Korea regularly ratchets up its hostile rhetoric around the time of the joint U.S.-South Korea military exercises, which usually spark a sharp surge in tensions on the divided peninsula.

As the double exercises began last year, North Korean leader Kim Jong-Un urged his army to prepare for war with the United States and its allies.

The reclusive state also fired two short-range ballistic missiles into the sea at the start of the exercises.