WASHINGTON- The United States said that while al Qaeda's Pakistan-based "core organization" had been severely degraded, affiliates of the militant group in Africa and the Middle East were becoming more "operationally autonomous" and aggressive.

The State Department said in its annual global report on terrorism that the central organization of al Qaeda, under the leadership of Ayman al Zawahiri, had been "much diminished" by international efforts and had lost many of its senior leaders.

But the report said instability and weak governments in the Middle East and North Africa had enabled al Qaeda affiliates and like-minded groups to "broaden and deepen their operations" in Yemen, Syria, Iraq, North Africa and Somalia.

Groups such as the Afghan and Pakistani Taliban and the Haqqani network continue to attack American and local targets on both sides of the Afghan/Pakistani border, and the Pakistan-based Lashkar-e-Tayyiba believe U.S. interests are "legitimate targets for attacks," the report said.

Thousands of militants, some of them English-speaking, have traveled to Syria to train and fight with groups fighting President Bashar al-Assad, according to the report.

Some have joined "violent extremist groups," and U.S. and other Western countries fear they may plot attacks when they return home, it said.

The report said various national authorities had estimated that in 2013, 90 militants went to Syria from Denmark, 184 from France, 240 from Germany, 30-40 from Norway, 100-200 from Belgium, and 75 from Sweden.