SEOUL - North Korea on Thursday fired two short-range missiles off its east coast amid already high tensions sparked by its nuclear test in May, South Korean military officials said.

They were launched from a base near the eastern port of Wonsan, a defence ministry spokesman said, with one fired at 5:20 pm (0820 GMT) and the other at 6:00 pm.

The hardline communist state has responded defiantly to UN condemnation of its long-range rocket launch on April 5 and its May 25 nuclear test, vowing to bolster its defenses.

"They appear to be ground-to-ship missiles, which were launched into the East Sea (Sea of Japan)," the spokesman told AFP.

"We have no detailed information now but there have been preparations for missile launches in the region."

The North issued a fresh warning to Japan on Wednesday to stay clear of some coastal areas during military exercises until July 11.

According to Japan's Coast Guard, Pyongyang issued navigation bans for 10 areas in the Sea of Japan and the Yellow Sea, citing "military gunfire and bombardment training."

South Korea's JoongAng Ilbo newspaper, quoting an intelligence source, said the North in the coming days is likely to fire a series of short-range missiles.

Apart from ground-to-ship weapons with a range of 140 km (88 miles), it said these would likely include Scud-B missiles with a range of 340 kilometres.

The North may also fire Rodongs, whose 1,300-km range would likely be shortened to some 400 km for the current round of testing, the paper predicted.