US Defence Secretary Chuck Hagel has ordered an aircraft carrier to move into the Gulf in case military action is required in Iraq.
The carrier USS George H.W. Bush will be accompanied by the guided-missile cruiser USS Philippine Sea and the destroyer USS Truxtun.
Mr Hagel said the moving carrier will provide "additional flexibility" if military options are needed to deal with the crisis in order to "protect American lives, citizens and interests in Iraq".
The ships are expected to arrive in the Gulf later on Saturday.
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."