NEW YORK - The United States has begun striking targets of the Islamic State in Syria, without authorization from the government of Bashar Assad in Damascus but in conjunction with "partner forces," the Pentagon said on Monday night."US military and partner nation forces are undertaking military action against ISIL [Islamic State] terrorists in Syria using a mix of fighter, bomber and Tomahawk Land Attack Missiles," Pentagon Secretary Rear Admiral John Kirby said in a statement. "Given that these operations are ongoing, we are not in a position to provide additional details at this time."US President Barack Obama made the decision to begin air strikes against the group, which holds court in Raqqa, eastern Syria, earlier in the day.Syrian opposition leader Hadi al-Bahra sat next to US Secretary of State John Kerry on Monday night at the Metropolitan Museum of Art, highlighting the pillaging of Syrian cultural heritage, before the strikes occurred.The Obama administration has not specified which partner countries participated in the strikes. But Kerry noted on Monday morning that the US-led coalition against Islamic State encompassed 50 nations, and US ambassador to the United Nations Samantha Power on Sunday said the US would likely strike Syria with help.A US official told Reuters that Arab partners are helping in ongoing air strikes against Islamic State targets in Syria.The official, who spoke on condition of anonymity, declined to say which nations were involved or specify their roles.Reuters contributed to this report.