IP - North Korea fired suspected short-range ballistic missiles off its east coast on Friday, South Korea’s military said, a day after South Korea and the U.S. flew powerful fighter jets in a joint drill that the North views as a major security threat.

Iran PressAsia: South Korea’s Joint Chiefs of Staff said the launches were made from the North’s east coast Wonsan region around 3:10 p.m.

It said South Korea’s military had bolstered its surveillance posture and was maintaining readiness.

In recent months, North Korea has extended its run of weapons testing as part of its efforts to enlarge and modernize its arsenal while diplomacy with the United States and South Korea remains dormant.

Last week, North Korean leader Kim Jong Un supervised the test firing of a new multiple rocket launch system, according to the North’s state media.

North Korea says it has been forced to boost its nuclear and missile programs to deal with U.S.-led hostilities.

North Korea cites expanded U.S.-South Korean military training, which it calls an invasion rehearsal.

Many foreign experts say North Korea uses its rivals’ military drills as a pretext for building a larger weapons arsenal in the belief that it would boost its leverage in future diplomacy with the U.S.

On Thursday, two South Korean F-35As and two U.S. F-22 Raptors were mobilized for combined aerial exercises over the central region of South Korea.