US secretary of state John Kerry said American support for Iraqi security forces will be "intense and sustained" to help them combat the Islamist insurgency that has swept through the country's north and west.
Isis, he said, was "fighting to divide Iraq and to destroy Iraq - so this is a critical moment for Iraq's future."
Speaking in Baghdad, he said Iraq's leaders must meet the "existential threat" by immediately taking a stand united against the Islamist group and quickly forming a new, " genuinely inclusive government."
He added that rise of Isis "threatens the stability of the entire region and it is a threat also to the United States and to the West."
The Foreign Secretary has been clear on the threat of Isis, but he has ruled out the prospect of any UK military involvement in the crisis.
Iraq’s foreign minister, Hoshyar Zebari, is a natural diplomat. Polite, immaculately dressed, and blessed with a great memory.
Isis has paraded military equipment in Mosul it captured from when the Iraqi army fled in what some see as a "nightmare scenario."