The advanced, radar-evading F-22 Raptors were deployed to Osan Air Base, the main U.S. Air Force base in South Korea, from Japan to support ongoing bilateral exercises, the U.S. military command in South Korea said in a statement that urged North Korea to restrain itself.
"(North Korea) will achieve nothing by threats or provocations, which will only further isolate North Korea and undermine international efforts to ensure peace and stability in Northeast Asia," the statement said.
Saber-rattling on the Korean peninsula drew a plea for peace from Pope Francis, who in his first Easter Sunday address called for a diplomatic solution to the crisis on the Korean peninsula.
"Peace in Asia, above all on the Korean peninsula: may disagreements be overcome and a renewed spirit of reconciliation grow," he said, speaking in Italian.
Tensions have been high since the North's young new leader, Kim Jong-un, ordered a nuclear weapons test in February, breaching U.N. sanctions and ignoring warnings from North Korea's closest ally, China, not to do so.
That test, North Korea's third since 2006, drew further U.N. and bilateral sanctions designed to pressure the impoverished North to stop its nuclear weapons program. Pyongyang responded to the new steps by ratcheting up warnings and threats of war.
North Korea said on Saturday it was entering a "state of war" with South Korea, but Seoul and its ally the United States played down the statement from the official KCNA news agency as the latest in a stream of tough talk from Pyongyang.
In a rare U.S. show of force aimed at North Korea, the United States on Thursday flew two radar-evading B-2 Spirit bombers on practice runs over South Korea.
On Friday, Kim signed an order putting the North's missile units on standby to attack U.S. military bases in South Korea and the Pacific, after the stealth bomber flights.
The F-22 jets will take part in the annual U.S.-South Korea Foal Eagle military drills, which are designed to sharpen the allies' readiness to defend the South from an attack by North Korea, the U.S. military said.