The US and allies said to include Arab nations have launched the first air strikes against Islamic State (IS) militants in Syria, the Pentagon says.
Spokesman Rear Adm John Kirby said fighter and bomber jets and Tomahawk missiles were used in the attack.
The strikes were expected as part of President Barack Obama’s pledge to “degrade and destroy” IS, which has taken huge swathes of Syria and Iraq.
The US has already launched 190 air strikes in Iraq since August.
However, Monday’s action expands the campaign against the militant group across the border into Syria.
Rear Adm Kirby confirmed the strikes, saying “US military and partner nation forces” were undertaking military action in Syria – but did not give details.
“Given that these operations are ongoing, we are not in a position to provide additional details at this time,” he said in a statement.
The Syrian government has not formally consented to the air strikes on its territory. However, it says it was informed before they took place.
Reports indicate many of the strikes hit Raqqa province, an IS stronghold in eastern Syria the group captured in 2013.
The Syrian Observatory for Human Rights, which has a network of activists on the ground, said more than 20 militants were killed in two strikes on IS positions in Raqqa.
‘Bombing without consent’
US media reports said Bahrain, Jordan, Qatar, Saudi Arabia and the United Arab Emirates were among those involved alongside the US. Jordan confirmed it had taken part but gave no details on its role.
Analysts say it is significant that countries with a Sunni majority, such as Saudi Arabia, appear to be among those supporting US efforts against IS.
IS members are jihadists who adhere to an extreme interpretation of Sunni Islam and consider themselves the only true believers.