It has come as an act of defiance towards the United States, further stoking regional tensions already high due to its nuclear test in May.

A South Korea news agency said the missile were Scuds, which would mark an escalation by the reclusive North, which has fired several non-ballistic, short-range missile since the May 25 nuclear test.

The news agency quoted an anonymous South Korean official as saying: "North Korea fired two missiles, which appeared to be a Scud type. The missiles are estimated to have the range of about 500 km (310 miles)."

Two similar missiles were fired at intervals over the next few hours, the government source said.

South Korean Defence Ministry sources confirmed the North fired five missiles off its east coast that travelled for about 400 km, which would indicate it fired ballistic missiles. The sources would not confirm the type of missiles.