SEOUL, South Korea (CNN) -

North Korea fired two short-range missiles early Sunday toward waters east of the Korean Peninsula, the latest such launch in the tense region, a South Korean official said.

The projectiles were fired at 1:20 a.m. and 1:30 a.m. Sunday (12:20 p.m. and 12:30 p.m. ET Saturday), according to the South Korean defense ministry official. They appear to have flown about 500 kilometers (310 miles).

The official added that South Korea's military is monitoring the situation closely.

North Korea has carried out a series of missile and rocket launches into the sea in recent months, drawing criticism from South Korea, the United States and the United Nations.

South Korea and the United States, especially, have expressed concerns about both missile launches and that Pyongyang might be moving closer to developing nuclear weapons.

Prior to Sunday, the most recent launch happened Wednesday morning, according to a South Korean defense ministry official.

North Korea did not declare a no-fly zone prior to the launch, of what was assumed to be short-range ballistic missiles, from North Korea's western Hwanghae Province, the official said. No damage or injures were reported.