Federal authorities in the US city of Denver have arrested a woman accused of providing material assistance to Islamist militants Isis.
According to a criminal complaint filed with a court in the state of Colorado, Shannon Maureen Conley is accused of conspiring to commit an offence against the United States
The leader of the Islamic State, formerly Isis, has released the first audiotape calling for jihad since the group renamed.
Abu Bakr al-Baghdadi reportedly said in an audio message posted online:
There is no better effort in this blessed month or any, other than jihad in God's path, so embrace this change and champion Allah's religion through jihad.
Mr Obama said the additional personnel to reinforce security at the US Embassy, the Baghdad International Airport and other facilities, in light of the ongoing security situation in the country.
Extra security forces, rotary-wing aircraft as well as intelligence and surveillance support were being sent as part of the deployment.
"This force is deploying for the purpose of protecting US citizens and property, if necessary, and is equipped for combat," Mr Obama said in a letter to the speaker of the House of Representatives.
"This force will remain in Iraq until the security situation becomes such that it is no longer needed."
The declaration of caliphate by Isis - which is now calling itself Islamic State - is a message that Islamic state militants have become a threat to all countries, an Iraq military spokesman has said.
"This declaration is a message by Islamic State not only to Iraq or Syria but to the region and the world," Iraqi army spokesman Qassim Atta told Reuters. "The message is that Islamic State has become a threat to all countries."
"I believe all the countries, once they read the declaration will change their attitudes because it orders everybody to be loyal to it," he added.
Supporters of Isis - which is now calling itself Islamic State - were filmed firing celebratory shots into the air in a parade in the eastern Syrian city of Raqqa, as the group announced the declaration of the caliphate.
Israeli Prime Minister Benjamin Netanyahu said he supported a push for Kurdish statehood, a position that appears to clash with America's preference to keep Iraq united.
He told Tel Aviv University's INSS think tank: "We should... support the Kurdish aspiration for independence."
He also outlined what he described as the collapse of Iraq and other Middle East regions under strife between Sunni and Shiite Muslims.
Militants from Isis - which is now calling itself Islamic State - called on all Muslims to pledge allegiance to their leader Abu Bakr al-Baghdadi in a statement posted on jihadi websites.
They said: "It is incumbent upon all Muslims to pledge allegiance to (him) and support him...The legality of all emirates, groups, states, and organizations, becomes null by the expansion of the khalifah's (Caliph's) authority and arrival of its troops to their areas."
Isis militants battling government forces in both Iraq and Syria have declared an Islamic "Caliphate" in the swathes of territory it has captured in both countries.
In a statement posted on jihadist websites, the al-Qaida offshoot known said they had changed their name from the Islamic State in Iraq and the Levant to 'Islamic State'. Its leader Abu Bakr al-Baghdadi is "Caliph" - the head of the state, the statement said.
the group's spokesman Abu Muhammad al-Adnani said in the statement which was translated into several languages: "He is the imam and khalifah (Caliph) for the Muslims everywhere."
President Obama voiced his concerns about Isis rebels returning to wage war in the west as Islamist militants continued to battle government forces in Iraq.
The US leader said: "We've seen Europeans who are sympathetic to their cause travelling into Syria and now may travel into Iraq getting battle hardened. Then they come back. They've got European passports. They don't need a visa to get into the United States."
Meanwhile, Iraq took deliver of some second hand fighter jets which they hope will help them to halt the advance of the militant fighters.
The Iraqi government received a boost in its fight against militants with the delivery in Baghdad of the first batch of five Russian-made Sukhoi jets, according to EBU.
Two Iraqi security officials confirmed arrival of the planes, which Iraqi purchased secondhand from Russia.
Meanwhile, the Iraqi government launched its biggest push yet to wrest back ground lost to Sunni militants, as soldiers backed by tanks and helicopter gunships began an offensive to retake the northern city of Tikrit.