(Updates with South Korea defence ministry)
SEOUL, March 16 North Korea fired 25 short-range rockets into the sea off the east of the Korean peninsula on Sunday, an unusually large number but they were obsolete weapons, probably 40 years old, South Korea's Defence Ministry said.
South Korea's Yonhap news agency earlier reported that the North had fired 10 rockets that flew 70 km (45 miles) before splashing into the sea.
North Korea is not banned from short-range missile launches under U.N. sanctions and frequently tests its arsenal.
South Korea's Defence Ministry spokesman Kim Min-seok said it was likely because of the age of the rockets that the North fired a barrage of them in one day, and they were hardly the destructive weapons that they may have been in the 1960s.
"But there's no question in our view that it's a provocative action and a show of force that they fired that many," Kim said, adding the North had put aircrafts and vessels that may have been in the area in grave danger by issuing no advance warning.
The U.S. State Department said it was closely monitoring the situation after the reports of the missile firing.
"We once again call on North Korea to refrain from provocative actions that aggravate tensions," State Department spokeswoman Jen Psaki said in a brief statement.
The North has toned down its bellicose rhetoric towards the South, although it has denounced annual joint U.S.-South Korean military exercises that are currently taking place.
It undertook a series of short-range missile launches earlier this month as the joint exercises, which North Korea views as a threat to its security, started.
In early 2013, North Korea conducted its third nuclear weapons test, having successfully launched a long-range rocket in 2012 that critics say was aimed at proving technology for an intercontinental ballistic missile.
Both of those are banned under U.N. sanctions. (Reporting by David Chance and Jack Kim; Additional reporting by Arshad Mohammed in Washington; Editing by Robert Birsel, Peter Cooney and Michael Perry)