North Korea fired off short-range missiles into the East Sea on Friday amid heightened tension following its February nuclear test, a military source in Seoul said.

"A North Korean military unit on drill test-fired two shots of short-range missiles, presumed to be KN-02 missiles, into the East Sea" the source said.

The source did not say the exact time of the launching.

"The launch was seen as testing its capability for short-range missiles. It seemed to be conducted on a military-unit level, not at a national level."

North Korea is ratcheting up war rhetoric almost daily in response to the U.N. Security Council's adoption of new sanctions for the country's Feb. 12 nuke test.

Pyongyang is believed to have more than 1,000 missiles -- most of which are able to strike South Korea -- and some are capable of hitting Japanese and U.S. military bases in this region. The KN-02 missiles, an upgraded version of SS-21 short-range missiles, are estimated to have a range of about 120 kilometers.

The South Korean military source said the North's missile launch appears to be in response to the joint South Korea-U.S. Foal Eagle and Key Resolve military exercises that began on Monday.

According to North Korean media reports, the North's leader Kim Jong-un oversaw artillery exercises this week that targeted two South Korean frontline islands in the Yellow Sea.

Meanwhile, North Korea warned that it would be advisable for residents in several islands near the maritime border in the Yellow Sea to evacuate, according to Uriminzokkiri, North Korea's propaganda Web site.

In November 2010, North Korea launched artillery shelling on South Korea's Yeonpyeong Island near the tense maritime border. The attack killed four people, including two civilians, and injured 18 others.

The year of 2013 also marks the third anniversary of the sinking of a South Korean navy ship by Pyongyang's torpedo attack in the Yellow Sea, killing nearly 50 sailors. (Yonhap News)