President Barack Obama is ordering another 350 U.S. military personnel to Iraq to protect American diplomats and facilities in Baghdad.
State Department spokeswoman Marie Harf says the additional forces will not take on a combat role, but because diplomatic officials made the request for more security.
The United States has been targeting Islamic State militants in Iraq with airstrikes. Obama has said U.S. forces will continue such action to protect American interests in Iraq from the militants.
The Islamic State group has seized large parts of northern Iraq and Syria, and has threatened to overrun the Iraqi capital.
President Obama is on his way to a NATO summit in Wales. He will consult with U.S. allies on an international coalition to implement a strategy in the fight against Islamic State.
Earlier Tuesday in Baghdad, angry relatives of Iraqi soldiers abducted by Islamic State militants in June stormed parliament, demanding information.
Many of the relatives plan to attend a special session of parliament Wednesday when lawmakers will discuss the matter.
In a new report, Amnesty International accuses the Islamic State of "ethnic cleansing on a historic scale," in a bid to wipe out non-Arabs and non-Sunni Muslims.
The report says the systematic campaign includes hundreds of mass killings and perhaps thousands of abductions that have terrorized all of northern Iraq, and fueled sectarian tensions in the region.
Survivors quoted in the report say some people severely wounded in the massacres were left where they were shot, doomed to suffer a slow and agonizing death. The report said the militants have been shooting men to death but are also kidnapping hundreds of women and children.
The United Nations has issued a similar warning about minority persecution at the hands of the Islamic State group.
Some information for this report comes from AFP.