Seoul, March 28 : A nuclear-powered US aircraft carrier arrived in South Korea's port city of Busan on Tuesday amid growing North Korean threats. The USS Nimitz carrier docked at ROK Fleet Command in the city, 325 km southeast of Seoul, after its strike group trained with the South Korean Navy in the international waters south of the southern island of Jeju the previous day, reports Yonhap NewsAgency. Its presence here is expected to send a warning to Pyongyang, which has been ratcheting up tensions through missile launches and repeated threats to use nuclear weapons in a contingency, observers said. The flat-top is the flagship of Carrier Strike Group 11, which includes USS Bunker Hill, a Ticonderoga-class guided missile cruiser; and two Arleigh Burke-class destroyers, USS Wayne E. Meyer and USS Decatur. It has brought some 70 combat aircraft, including F/A-18 fighters and E-2 Hawkeye early warning aircraft. On the eve of its port call in Busan, the North fired what it claimed to be "tactical" ballistic missiles loaded with simulated "nuclear warheads". The launch followed a series of earlier weapons tests, including that of an "underwater nuclear attack drone". Addressing reporters aboard the USS Nimitz on Monday, Rear Adm. Christopher Sweeney, the commander of the carrier strike group, highlighted the allies' readiness to deal with North Korean threats, according to a pool report. "I'm not threatened or worried about North Korea," he said, noting that the US has "deployable strategic assets at the ready on every day". /IANS