US President Barack Obama said Tuesday that destroying the Islamic State (IS) group remains his "top priority" at a time when the jihadist group continues to lose ground in Iraq and Syria.

"We continue to take on their leadership, their financial networks, their infrastructure," Obama said at a meeting with senior military officials in the White House.

"We are going to squeeze them and we will defeat them."

"As we've seen from Turkey to Belgium, ISIL still has the ability to launch serious terrorist attacks," he added, using another term for the IS group.

Coalition forces must maintain pressure on the insurgents using diplomacy and intelligence as well as military operations, coordinating operations between various branches of government, he said.

"We can no longer tolerate the kinds of positioning that is enabled by them having headquarters in Raqqa and in Mosul," he said of cities in Syria and Iraq.

"Destroying ISIL continues to be my top priority."

Obama spoke next to Defense Secretary Ash Carter, General Joe Dunford, chairman of the Joint Chiefs of Staff, and combatant commanders.

Carter on Tuesday proposed changes to the military that would streamline its various forces of some 1.3 million soldiers and boost their ability to respond quickly by reviewing the current "top heavy" structure set out in the 30-year-old Goldwater-Nichols Act, which critics say is outdated.

The fight against the Islamic State group has shown that the military's various commands and special forces should better coordinate their efforts, he said.

"We intend to be more efficient by integrating functions like logistics, intelligence and plans," he said.

Washington has led an international coalition staging airstrikes against the IS group in Syria and Iraq since September 2014, parallel to operations by the Syrian government and its ally Russia.

The Syrian army and its allies on Monday retook Syria's central town of al-Qaryatain, one of the IS group's last strongholds in the region.

The operation 75 miles (120 kilometers) southwest of Palmyra helped secure the government's retaking of that ancient city last week after the Islamic State group held it for 10 months, destroying important archaeological sites and executing 280 people.