BAGHDAD—Syrian warplanes carried out airstrikes in western Iraq, stepping up the military role of the U.S. adversary in helping Baghdad's Shiite-dominated government fight Sunni insurgents.

The strikes on Tuesday came as the Pentagon announced that the first 130 members of a potential 300 U.S. military advisers were in place in Baghdad to start assessing and improving the Iraqi army's ability to counter the gains of rebels led by the Islamic State of Iraq and al-Sham.

At least 50 people were killed and more than 132 others wounded Tuesday when missiles fired from what appeared to be Syrian government planes hit a municipal building, a market and a bank in the district of Al Rutba, according to an Anbar provincial official and Mohammed Al Qubaisi, a doctor in the district's main hospital.

Those people said Tuesday was the second consecutive day of airstrikes by Syria, which has joined Iran in aiding the embattled Baghdad government against the ISIS-led rebels. Tehran has deployed special forces to help protect the capital and the Iraqi cities of Najaf and Karbala, which Shiites revere.

There was no confirmation from Syrian authorities or Iraqi military air force officials that Syrian fighters had entered Iraqi airspace. Iraq's own air capabilities are decidedly limited and wouldn't be capable of carrying out such an attack. Reports of the Syrian attack were widely mentioned in the Iraqi media.