Baghdad (CNN) -- At least three explosions struck Friday near Baghdad's Green Zone, where a parade to mark Iraq's Army Day was taking place, witnesses said.
There were no immediate reports of casualties in the attacks, which come amid heightened security across the Iraqi capital in preparation for Army Day. Officials have said they were concerned about the possibility of attacks.
Witnesses said the explosions were caused by mortars or rockets that struck a short stretch of road between the Foreign Ministry and one of the main checkpoints leading into the Green Zone, areas previously targeted in attacks.
The Green Zone, also known as the International Zone, is home to the U.S. Embassy and a number of Iraqi government and military offices.
Prime Minister Nuri al-Maliki and other top officials attended the parade.
January 6 is the anniversary of the formation of the Iraqi Army. This is the first time Iraq has marked the occasion since the 2003 invasion without U.S. troops in the country.
The latest attacks came after dozens of people died Thursday in bombings in Baghdad and near Nasiriya, strikes thought to be targeting Shiites.
Violence raged for years after the U.S. invasion of Iraq between members of the country's Sunni minority, who held power during the era of Saddam Hussein, and its Shiite majority, which gained power after his ouster.
Sectarian violence eventually diminished. But in recent weeks, Iraqis have been concerned about an increase in Sunni-Shiite violence after the U.S. military withdrawal from the country last month.
Sunnis in Iraq have felt marginalized by the government of Prime Minister Nuri al-Maliki, a Shiite. That anger intensified after he ordered the arrest last month of Sunni Vice President Tariq al-Hashimi, who was charged with ordering bombings and assassinations, a charge he denies.