Seoul: Four times as many US 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 on Thursday.

The US will send 15,000 troops to the annual computer-simulated ‘Key Resolve’ exercise, the Yonhap news agency quoted Defence 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 US 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 US-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.

Last month, North Korea conducted its fourth nuclear test despite international condemnation and followed it with a long-range rocket launch on February 7. The launch was widely condemned as a ballistic missile test banned under UN resolutions.

Military muscle-flexing

The United States and South Korea have responded with a series of military muscle-flexing activities.

On Monday, the USS North Carolina attack submarine arrived at the southern port of Busan for joint training with the South Korean navy.

And four US F-22 stealth fighters were deployed to an air base near Seoul on Wednesday.

South Korea and the US are also set to begin talks this week on the possible deployment of an advanced US missile defence system, despite opposition from China.

The US Terminal High Altitude Area Defence System (THAAD) would fire anti-ballistic missiles into the sky to smash into enemy rockets during their final flight phase.

‘We will exercise our sovereign rights regarding this issue and in making decisions’, Moon told journalists.

‘Nothing is more important than taking measures to protect the people and their assets from the increasing nuclear and missile threats from North Korea’, he said.

South Korean President Park Geun-Hye on Tuesday signalled a tough new approach to derailing North Korea’s nuclear weapons programme and indicated the South would lead efforts to bring about regime change in the Stalinist state.

Seoul last week abruptly withdrew from the Kaesong industrial complex, where South Korean firms operated factories that employed North Korean workers, arguing hard currency from the symbol of cooperation with the North is believed to have been diverted to weapons development.

South Korean foreign ministry spokesman Cho June-Hyuck said Thursday that Seoul is also seeking international cooperation to curb North Korean immigrant workers.

Some 60,000 North Koreans are working in China, Russia, the Middle East and Southeast Asia, Yonhap said.