A senior military official, speaking on condition of anonymity, told AFP that the drones were not Reapers or Predators but they are smaller Shadow robotic aircraft launched from a catapult.

The Shadow aircraft, US forces have used in Iraq and in Afghanistan in the past, are about 14 feet (4 meters) long and can fly up to 8,000 feet (2,400 meters) above the ground level.

Pentagon press secretary Rear Admiral John Kirby told a news conference on Tuesday that US troops would "help provide extra security for our facilities, our people, our property, and to also allow - to help allow the State Department and the embassy to continue to function as it is."

Kirby added that the troops will work to safeguard access to the Baghdad airport and the US embassy, adding the embassy remains "open".

He went on to say that the situation "continues to be very dangerous" and "the threat continues to be very real."

The United States says it has so far sent 500 troops to Baghdad to increase security for its embassy there.

On Monday, President Barack Obama also ordered 200 more troops to Baghdad to protect American diplomats as well as other personnel working in the city.

Over the past weeks, militants from the so-called Islamic State of Iraq and the Levant (ISIL) -- an al-Qaeda splinter group that enjoys the support of loyalists of Iraq’s former Baathist regime -- have been wreaking havoc in Iraq.

The ISIL has captured large swaths of territory across northern Iraq after seizing the city of Mosul on June 10.

The Takfiri militants, who have posted pictures of their atrocious acts against Iraqi citizens online, have vowed to continue their offensive towards the capital Baghdad.

BA/BA