People hold South Korean flags in Seoul March 1, 2009. REUTERS/Lee Jae-Won

SEOUL (Reuters) - South Korea is acquiring 40 U.S.-made missiles for an Aegis destroyer this month to boost its defenses amid reports North Korea may soon test-fire missiles, Yonhap news agency on Sunday quoted a military source as saying.

North Korea, which rattled regional security with a May 25 nuclear test, is preparing to test a long-range missile that could hit U.S. territory and mid-range missiles that could hit all of South Korea, a South Korean presidential Blue House official said last week.

The surface-to-air missiles for the Aegis destroyer, designed to track and shoot down objects including missiles, can hit targets up to 160 km (100 miles) away, Yonhap quoted the source as saying.

North Korea has also warned ships to stay away from waters off its east coast city of Wonsan, Japan’s Coast Guard said last week, in a possible indication of a missile test.

North Korea launched in April a rocket it said was carrying a satellite. The move was widely seen as a disguised test of its long-range Taepodong-2 missile and a violation of U.N. resolutions barring the reclusive state from ballistic missile testing.

The U.N. Security Council punished it for the missile launch by tightening existing sanctions and imposing new ones after the nuclear test to halt its arms trading, one of the few items the cash-short state with a broken down economy can export.

The U.S. Navy has said it is monitoring a North Korean ship under the new U.N. security resolutions imposed after the nuclear test. A South Korean intelligence source said the ship is likely carrying missiles and parts, and it could be heading to Myanmar, broadcaster YTN said.

At the weekend, the prickly North warned in an official media report it would shoot down any Japanese military plane that breached North Korean air space.

South Korean officials have said the North’s recent saber rattling may be a way for leader Kim Jong-il to build internal support as he prepares for succession in Asia’s only communist dynasty.