At least five rockets were fired from northern Iraq at a military base in Syria housing a US-led coalition on April 21, making it the first major attack against the coalition forces in several weeks.
A US official told Reuters news agency that no personnel were injured. Iraqi security forces accused outlawed elements of having targetted the military base.
The attack against US forces is the first since early February when Iranian-backed groups in Iraq stopped their attacks against US troops.
It comes days after Israel reportedly responded to an Iranian attack with a drone strike on the Islamic republic, amid tensions fuelled by the Gaza war.
According to AFP, the Iraqi security forces accused "outlaw elements of having targetted a base of the international coalition with rockets in the heart of Syrian territory", at around 9:50 pm (1850 GMT).
The security forces burned the vehicle involved in the attack, the statement added.
Rami Abdel Rahman, director of the Syrian Observatory for Human Rights war monitor, said several rockets had been fired "from Iraqi territory at the Kharab al-Jir base" in northeast Syria, where US forces are stationed.
He accused the Islamic Resistance in Iraq, a loose alliance of Iran-backed groups, of staging the attack.
The group has claimed most of the attacks on US forces carried between mid-October and early February.
Following a series of rocket attacks and drone strikes by pro-Iran armed factions against US soldiers deployed in the Middle East over the winter, there had been several weeks of calm.
The Islamic Resistance in Iraq has said it is acting in solidarity with Palestinians and out of anger at US support for Israel in the Gaza war.
The United States has around 2,500 soldiers stationed in Iraq and nearly 900 across the border in Syria as part of an international coalition created in 2014 to fight the Islamic State group (IS).
Sunday night's rocket attack came against the background of increasing tension in the region, with a flare-up between Iran and Israel.
Early on Saturday, an explosion at an Iraqi military base killed one person and wounded eight others.
Security forces said the blast hit the Kalsu military base in Babylon province south of Baghdad, where regular army, police and members of Iraq's Popular Mobilisation Forces, or Hashed al-Shaabi, are stationed.
CENTCOM, the US military command in the region, denied involvement in a strike there. The Israeli army refused to comment.