The United States is sending two dozen long-range bombers to Guam in the western Pacific as a further deterrent against North Korea, US defence officials said tonight.
The force will consist of a dozen B-52s bombers and a dozen B-1 bombers.
The United States said earlier that it will protest a weekend incident in which North Korean fighter jets intercepted a US surveillance plane, calling it "reckless behavior" by Pyongyang.
"This kind of reckless behavior by North Korea" will only lead to "further isolation" of the Stalinist regime by the international community, White House spokesman Mr Ari Fleischer told reporters.
Four North Korean jets intercepted a US Air Force RC-135 reconnaissance plane in international airspace over the Sea of Japan on Sunday and came within 50 feet of the big American jet while shadowing it, the Pentagon said.
The North Korean jets shadowed the US aircraft for about 20 minutes, said a Pentagon spokesman.
The spokesman said initially one of the North Korean jets had locked on to the RC-135 with its fire-control radar, but later said that was not certain and the US Defence Department was checking tapes of the incident.
The encounter followed repeated assertions by North Korea's state media that RC-135s had been flying sorties inside its airspace.
Pyongyang said they showed the United States was preparing for war on the peninsula.
Tensions have risen on the Korean peninsula over the North's suspected nuclear arms ambitions, and as the United States builds up military forces in the Gulf in preparation for a possible invasion of Iraq.
North Korea and the United States have no diplomatic relations.