North Korea fired multiple short-range ballistic missiles toward the sea off its eastern coast, the South Korean military said Friday, just hours after the powerful sister of the North's leader denied allegations of sending weapons to Russia.

The South Korean military did not immediately provide more details, including the distance traveled. Japan's Defense Ministry did not report the launches, but government officials told NHK that the weapons were likely short-range.

"Our military has ramped up monitoring and vigilance against additional launches, while closely sharing information related to North Korean ballistic missiles with the U.S. and Japanese authorities," the South Korean Joint Chiefs of Staff said in a statement.

Earlier Friday, Kim Yo Jong, the sister of North Korean leader Kim Jong Un, said in a statement carried by state-run media that her country's ballistic missiles were intended solely as a deterrent against South Korean military moves, denying that Pyongyang was exporting the weapons.

Friday's launches also come just a day after the South Korean and U.S. militaries held joint drills involving advanced stealth fighter jets.

North Korea has conducted a spate of weapons tests this year, including its first drills simulating a nuclear counterattack under its “nuclear trigger” management system in an exercise overseen by Kim Jong Un in April.

Late last month, the North conducted a test of a large liquid-fueled rocket engine, according to an analysis of imagery by a U.S. think tank, with Pyongyang appearing to be gearing up for another spy satellite launch soon.

North Korea successfully launched its first military reconnaissance satellite last November after two earlier failures. Days later, the country said that it would launch three additional spy satellites sometime this year.