General Joseph Dunford in Washington, July 9, 2015. REUTERS/Yuri Gripas/Files

WASHINGTON: The heads of the US and South Korean militaries discussed "military response options" after North Korea test launched an intercontinental ballistic missile, the Pentagon said Friday.

General Joe Dunford, who is Chairman of the Joint Chiefs of Staff, and Admiral Harry Harris, who heads the US military's Pacific Command, spoke with South Korea's Joint Chiefs of Staff Chairman, General Lee Sun Jin.

"During the call, Dunford and Harris expressed the ironclad commitment to the US-Republic of Korea alliance," Dunford spokesman Captain Greg Hicks said in a statement.

"The three leaders also discussed military response options."

While the Pentagon has long planned for the possibility of conflict with North Korea, the blunt language in the statement marked a departure from previous public reactions to missile tests.

Those earlier reactions typically decried the tests but did not emphasise military options.

It was the first time Dunford, who has been in his position for two years, had issued a statement raising military options, though he has discussed the topic in public conversations.

Pentagon chief Jim Mattis, who is currently on vacation, slammed North Korea's first test launch of an ICBM on July 4 as a "provocation" but stressed then that the United States seeks a diplomatic solution to the standoff.

"We remain prepared to defend ourselves and our allies from any attack or provocation," Pentagon spokesman Captain Jeff Davis said.