Rockets struck near Baghdad airport on Thursday in what an exiled Iran opposition group said was an attack on their camp that left three dead and around 50 wounded.
Nasser Bandar, the head of Iraq's civil aviation authority said three rockets hit near a military site in the airport area, but that information on any casualties was not immediately available.
He said flights were not interrupted by the attack, "which was outside the limits of the civil airport".
Members of an Iranian opposition group who are based near the airport while waiting to be transferred out of Iraq said that they were the target.
Iran's exiled opposition group, the National Council of Resistance of Iran said in a statement on its website that "dozens of missiles" were fired on Camp Liberty.
"As of midnight local time, three residents, killed when dozens of missiles hit Camp Liberty, have been identified," said the statement.
The United States condemned the attack "in the strongest terms", State Department spokeswoman Jen Psaki said in a statement, adding Washington had been coordinating with the United Nations and Iraqi officials "to ensure swift and immediate treatment to the wounded".
Washington called on the Iraqi government "to take additional measures to secure the camp against further violence, including by immediately installing additional protective barriers, such as bunkers and T-walls," Psaki said.
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The former US military base is home to some 3,000 members of Iran's main opposition group, the People's Mujahedeen Organisation of Iran.
The PMOI was founded in the 1960s to oppose the shah of Iran and later the country's clerical rulers.
The group set up camp in Iraq during Saddam Hussein's war with Iran in the 1980s, but was disarmed after the US-led invasion of Iraq in 2003 toppled Hussein, and today's Shia-majority and Iran-friendly government in Baghdad is eager to see it move elsewhere.
In September, 52 members of the PMOI were killed at their main former Camp Ashraf in Diyala province.
Authorities blamed infighting within the PMOI for the deaths while the opposition group claimed Iraqi forces entered the camp, killed 52 of its members and set fire to the group's property and goods.
UN rights experts said earlier this month those killed had been shot, many of them with their hands tied behind their backs.
Most of the camp's residents had already been relocated to Camp Liberty at the time of the attack.
Scores of PMOI members have been killed in more than a dozen attacks on their camps since US troops withdrew from Iraq at the end of 2011.
Violence in Iraq has reached a level not seen since 2008, when the country was just emerging from a brutal sectarian conflict.
More than 6,700 people have been killed in Iraq since the beginning of 2013, according to AFP figures based on security and medical sources.