A rocket fired by North Korea early Wednesday, which the US called an intercontinental ballistic missile, is thought to have fallen within Japan's exclusive economic zone (EEZ), Japan's defence ministry said.

"We presume that it fell within our EEZ," the country's defence minister Itsunori Onodera told reporters.

The Pentagon said the missile flew about 1,000 kilometers (620 miles) before splashing down in the Sea of Japan.