John Kerry (C) participates in the OSCE Ministerial Council meeting in Belgrade.

BELGRADE — Syrian and other Arab ground forces must be found to take on ISIS, Secretary of State John Kerry said on Thursday, saying the militant group would not be defeated by air strikes alone.

Kerry was speaking hours after Britain began bombing ISIS targets in Syria, joining forces with France and the United States, nearly three weeks after the jihadist group killed 130 people in attacks across Paris.

British Prime Minister David Cameron said there are as many as 70,000 moderate opposition fighters in Syria ready to take on ISIS with the help of foreign air strikes, an assertion opponents of the bombing campaign have questioned.

Kerry suggested that if a political solution could end the fighting between the government of Syrian President Bashar al-Assad and opposition groups and sufficient ground troops could be mustered, the militant group could be vanquished in months.

“I think we know that without the ability to find some ground forces that are prepared to take on Daesh, this will not be won completely from the air,” Kerry said, using an Arabic term for the jihadist group.

Asked later if he meant Western ground forces, Kerry said after a meeting in Belgrade of the Organization for Security and Cooperation in Europe (OSCE): “(I’m) talking about Syrian and Arab, as we have been consistently.”