North Korea test-fires 3 short-range missiles, South Korea says

SEOUL, South Korea (CNN) - North Korea test-fired three short-range missiles off its east coast Thursday, South Korea's Defense Ministry said.

The first two were fired about 40 minutes apart, a ministry spokesman said, according to South Korea's Yonhap news agency. It is unclear what time the third missile was launched.

A U.S. official told CNN "the missile firings come as no surprise."

"The North has been carrying out provocative acts for some time," said the official who did not want to be named for security reasons. "North Korea needs to stop this type of activity and return to the process of bringing about a denuclearization of the Korean peninsula."

North Korea had issued a warning to mariners to avoid an area in the Sea of Japan at certain times between June 24 and July 9 because of a "military firing exercise," according to a U.S. military communication about the warning provided to CNN.

The North issued a similar warning before testing a long-range missile in April, but that warning indicated two potential danger areas more indicative of a long-range missile test.

Thursday's reported test comes amid heightened tensions on the Korean peninsula. North Korea conducted a nuclear test in May, fired test rockets and threatened U.S. and South Korean ships near its territorial waters.