Jordanian warplanes carried out a bombing raid against the Islamic State group in Syria on Wednesday as part of a second day of US-led air strikes against the jihadists, two US defense officials told AFP.
"Jordan conducted an air strike overnight," said one of the officials, who spoke on condition of anonymity.
The raid was in addition to a US bombing run announced earlier by the American military's Central Command, the official said.
Pentagon officials offered no further details on the Jordanian air strike.
Jordan confirmed on Tuesday that it was taking part in the air campaign and four other Arab states have said they are participating: Bahrain, Qatar, Saudi Arabia and the United Arab Emirates.
US officials say Arab coalition aircraft dropped bombs in the first round of strikes launched early Tuesday but have not provided details of each country's role.
Although US aircraft are responsible for the vast majority of strikes on the IS group, the participation of the Sunni-ruled Arab countries carries symbolic weight and Washington sees it as crucial.
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The Arab partners have denounced IS extremists but also deeply oppose the Syrian regime led by President Bashar al-Assad, who is backed by their rivals in Shiite-ruled Iran.
Apart from the Jordanian raid on Wednesday, a US air strike in the past 24 hours damaged eight IS vehicles northwest of the Iraqi border town of Al-Qaim, officials said.
US aircraft have been bombing IS extremists in Iraq since August 8 in a bid to halt an advance by the militants that saw them seize large swaths of territory in Syria and Iraq.
The US bombing runs continued into Wednesday, with four raids bringing the total number of air strikes in Iraq to 198, according to US Central Command, which oversees American forces in the Middle East.
France recently joined the air campaign in Iraq.
In the latest air raids in Iraq, strikes west of the capital Baghdad hit two IS armed vehicles and an arms dump. Two more destroyed IS fighting positions threatening the Kurdish regional capital Arbil, Central Command said.
US aircraft have been targeting IS militants southwest of Baghdad recently because the group has been staging attacks in the area in an attempt to threaten the capital, said a second defense official, who asked not to be named.
"They've been probing and prodding there," the official said.