Seoul, Aug 10 (IANS): North Korea again fired two more projectiles believed to be short-range ballistic missiles into the East Sea on Saturday, South Korea's military said, the latest in a series of saber-rattling moves against the joint exercise between Seoul and Washington.

The projectiles were fired at 5.32 a.m. and 5.50 a.m. from its eastern coastal city of Hamhung in South Hamgyong province into the East Sea, and both flew around 400 km at a maximum altitude of 48 km and a top speed of around Mach 6.1, Yonhap News Agency quoted the Joint Chiefs of Staff (JCS) as saying.

"We see high chances of additional launches, as North Korea is now carrying out summertime drills and the combined exercise between South Korea and the US is underway," the JCS said in a statement.

"We have been closely monitoring the situation, while maintaining staunch military readiness."

Saturday marked the fifth such launch since July 25 when the North fired two short-range missiles.

The latest launch came just four days after the North fired two projectiles believed to be the newly developed short-range ballistic missiles known as KN-23 into the East Sea.

Such military moves appear to be a show of force against the combined military exercise between South Korea and the U.S., the presidential office Cheong Wa Dae said.

"Such a series of launches are feared to heighten military tensions on the Korean Peninsula, and we urge North Korea to stop such activities," the office added.

In Washington, a senior government official told Yonhap that the US was aware of the latest firing and is monitoring the situation closely with the allies.

Seoul and Washington kicked off their summertime military exercise on Monday, with the main part of the computer-based "Combined Command Post Training" set to begin on Sunday for a 10-day run.