Last Updated: Thursday, 7 June 2007, 11:38 GMT 12:38 UK
North Korea may have test-fired a number of short-range missiles off its west coast, South Korea's Yonhap news agency has quoted a source as saying.
The unnamed official said Seoul was investigating the reports and details of the tests.
Pyongyang test-fired at least one short-range missile at the end of May - off its east coast - as part of what appeared to be military exercises.
North Korea's military programme is a major source of international concern.
"We are confirming intelligence that North Korea fired short-range missiles into the West Sea on Thursday morning," the unidentified official was quoted by Yonhap as saying.
"We suspect the number of missiles fired today was one or two. We are working to distinguish the types of missiles."
The official said Thursday's suspected test off the west coast may have been carried out after a similar test failed on 25 May, when the North test-fired missiles off the east coast.
"It's seen as the North firing the missile that it didn't launch at that time," he said.
South Korea confirmed at least one missile was test-fired into the Sea of Japan on 25 May, although earlier reports suggested several had been fired.
It coincided with the launch of South Korea's first destroyer equipped with US-supplied high-tech Aegis radar.
Despite international alarm at the North's long-range missile and nuclear tests last year, the US and Pyongyang's regional neighbours played down the May test.
The US State Department described it as a "routine exercise" that would not affect six-party talks regarding the North's nuclear programme.
There has been no immediate reaction to Thursday's reported tests.
The tests come weeks after the North missed a deadline to shut down its Yongbyon nuclear reactor in return for economic and energy aid.
Pyongyang has refused to move forward on the deal until it has access to North Korean funds in a Macau bank, which had been frozen amid claims the money was linked to counterfeiting and money-laundering.