North Korea said the tests are preparations before an invasion. Allies say that the exercises, which last year made North Korea threaten to launch a nuclear war against South Korea and United States, are routine and defensive in nature.

Analysts say that North Korea is adopting a more flexible stance towards the United States and South Korea military exercises because they wants better relations with the outside world to revive their overwhelmed economy. Weeks of war rhetoric from Pyongyang toward Washington and Seoul last year followed international condemnation of its third nuclear test in February 2013.

North Korea launched Sunday 25 rockets with a range of 70 kilometers, which fell in international waters off the eastern coast of the country, according to the South Korean Defense Ministry. Career research showed that the rockets might be old Soviet controlled FROF models that North Korea has had since the 1960s, said Kim Min-seok, spokesman for the Ministry.

In Washington, Jen Psaki, spokeswoman for the State Department, urged North Korea not to take provocative actions that aggravate tensions.

Earlier this month, Seoul said that a cannonade of artillery from North Korea occurred minutes before a Chinese airliner apparently with 202 passengers flew in the same area.

Pyongyang argues that its missile tests are part of the regular training and take account of international navigation.

The US Government called on North Korea to refrain from “acts of provocation”, after which the North Koreans fired a total of 18 missiles towards the sea of Japan from its East Coast.

“We are aware of reports that North Korea fired several missiles into the sea,” said in a statement the spokesman of the State Department, Jen Psaki.

The spokesman added that the US “closely” follows the situation on the Korean peninsula and called, “once again” to North Korea to “refrain from acts of provocation that escalating tensions”.

This Sunday is the fourth test of this kind that the regime of North Korea carries out in the last three weeks.