SEOUL • Two American supersonic bombers flew over South Korea, one of which landed at a US base in a show of force that the United States said was aimed at reminding North Korea of its powerful military assets in the region.

Yesterday's flight came a day after Pyongyang claimed it had successfully tested a new, high-powered rocket engine which Seoul said was designed to demonstrate progress towards attaining a long- range missile.

On Sept 9, the North conducted its fifth nuclear test.

Television footage showed two supersonic B-1B Lancers flying low over the US Osan Air Base in Pyeongtaek, 64km south of Seoul.

One of the aircraft flew back to the Andersen Air Force Base in Guam, while the other landed at Osan, Yonhap news agency said.

"The bond between the United States and the Republic of Korea (South Korea) is iron-clad and the strength of that commitment will not be shaken by North Korea's aggressive behaviour," said Lieutenant General Thomas Bergeson of the US Air Force.

"What we are showing today is just one tool we have to choose from a wide array of options. The alliance grows stronger every day and we remain prepared to defend and to preserve the security of the Korean Peninsula and the region," he said.

The US has about 28,500 troops in South Korea.

On Tuesday last week, the US flew two planes over South Korea in a show of solidarity following Pyongyang's nuclear test, which was also condemned by China, the North's main diplomatic and economic benefactor.

The US Air Force said that yesterday's flight was the closest ever to North Korea made by a B-1 bomber.

The B-1 Lancer is a four-engine strategic bomber that can reach speeds of Mach 2. It is capable of carrying the largest payload of both guided and unguided weapons in the US Air Force inventory.

Next month, South Korea and the US will conduct a mock attack on a nuclear facility, CNN reported, quoting an official with the South Korean Defence Department.

Though the official said the drills were not aimed particularly at the North, the announcement followed recent nuclear-related moves by Pyongyang.

The US and South Korea are also expected to simulate what to do in the event of a sudden missile attack.

AGENCE FRANCE-PRESSE, REUTERS