SEOUL (Bloomberg) - South Korea's military fired warning shots across the military demarcation line at an unidentified object flying on Tuesday (May 23) afternoon, as tensions remained high on the peninsula days after another North Korea missile test.

The military is analysing the object's flight path, South Korea's Joint Chiefs of Staff said in a text message. Yonhap News reported that South Korea fired about 90 machine gun rounds across the border, and was checking whether the object was a drone.

Drone incursions have increased in recent years. In January 2016, a drone crossed the demarcation line, according to a Defence Ministry white paper released last year.

"In March and April 2014, small-sized drones believed to be from North Korea were found" in Paju, an island near the western sea border and the city of Samcheok, the report said.

Kim Young Woo, the chairman of the National Assembly's National Defence Committee, said that another unidentified object flying at a different speed appeared near Paju on Tuesday morning.

"There are various possibilities because different radars show different results," said Kim, who was briefed on the issue by the military. "The military mentioned that one of the two could have been a flock of birds."

North Korea fired a ballistic missile on Sunday (May 21) - its eighth such test of the year - in defiance of United Nations sanctions and warnings from US President Donald Trump.

The missile flew about 500km. Japan said it landed in in waters off its coast and didn't reach the nation's exclusive economic zone.

US Secretary of State Rex Tillerson called the ongoing testing "disappointing" and "disturbing".

But he said the US was in the early stages of applying economic and diplomatic pressure, and that perhaps North Korea was "acting out now in response to some of this pressure that I believe they're beginning to feel".