OSAN AIR BASE (South Korea) • Four United States F-22 stealth fighters flew across South Korea yesterday to an air base near Seoul, where they are being deployed in a show of force following North Korea's nuclear and missile tests.

Escorted by eight US and South Korean fighter jets, the radar-evading aircraft landed at Osan Air Base near Pyeongtaek city, 70km south of the border with North Korea.

Deployment of the F-22s, which are normally based on Okinawa in Japan, is the latest move by Washington to bolster defences in South Korea following the North's fourth nuclear test last month.

"This mission demonstrates the strength" of the US-South Korea alliance and "the resolve of both nations to maintain stability on the Korean Peninsula", Lieutenant-General Terrence O'Shaughnessy, commander of the US 7th Air Force, told journalists. He said the US maintained "an ironclad commitment" to the defence of South Korea.

Last month, the US flew a B-52 bomber capable of carrying nuclear weapons on a low-level flight over South Korea following the North's Jan 6 nuclear test.

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

A nuclear-powered aircraft carrier, the USS John C. Stennis, is also scheduled to join the annual South Korea-US military exercise slated for next month, Yonhap news agency said.

North Korea followed its latest nuclear test with a long-range rocket launch on Feb 7 that was widely condemned as a ballistic missile test banned under United Nations resolutions.

The military moves come as South Korea is due to begin talks with the US this week on the possible deployment of an advanced US missile defence system, which China and Russia have warned could undermine stability in East Asia.

Defence officials in Seoul and Washington say bringing the Terminal High Altitude Area Defence (Thaad) system to the South has become a clear necessity, given the progress North Korea is making on its ballistic missile programme.

"This is an effort to try and put in place a defensive system that will bolster security in the region. And we think it would be an appropriate step to take at this point," US Pentagon spokesman Peter Cook said on Tuesday.

China's Global Times, which has close ties to the ruling Communist Party, yesterday said that if South Korea insisted on deploying Thaad, China would install more missiles in the region and take "the highest-level precautions" against the system.

There are 28,500 US troops stationed in South Korea, which has more than 600,000 military personnel. The North has an army of 1.2 million.

AGENCE FRANCE-PRESSE, REUTERS