Al-Qaida affiliates in the Middle East and Africa are gaining strength and operational autonomy despite the weakening of the global terror outfit's Pakistan-based core, the US State Department has said.

International intervention has helped weaken the central leadership of al-Qaida over the years, but the terrorist organisation founded by Osama bin Laden has "evolved" and its affiliate organisations have regained the initiative over the years, the State Department's annual global report on terrorism said.

"Leadership losses in Pakistan, coupled with weak governance and instability in the Middle East and Northwest Africa, have accelerated the decentralisation of the movement and led to the affiliates in the AQ network becoming more operationally autonomous from core AQ and increasingly focused on local and regional objectives."

The report said the al-Qaida affiliates have become more aggressive following the degradation of the core leadership and outfits such as al-Qaida in the Arabian Peninsula (AQAP) and al-Qaida in the Islamic Maghreb (AQIM) have assumed bigger strike force.

Ironically, the report notes that US military intervention aiming to curb terror outfits in countries like Iraq and Libya have not been effective.

While Iraqi provinces such as Anbar and Nineveh have become the stronghold of the Islamic State of Iraq and the Levant (ISIL), Libya has become a "terrorist safe haven and its transit routes are used by various terrorist groups", the report said.

"These areas reportedly included camps, training centres, command headquarters, and stocks of weapons ... ISIL fighters allegedly controlled villages, oases, grazing areas, and valleys in these areas and were able to move with little impediment across international borders in the area."

The report also revealed hundreds of al-Qaida operatives and sympathisers from Europe travelled to conflict zones across the world, especially Syria, in the last year.

An estimated 400 Britons travelled to conflict zones during 2013 and at least 250 have been fighting alongside al-Qaida militants at any given time, the report said. It noted, citing various national government estimates, that at least 184 militants from France travelled to Syria while 240 from Germany and 90 from Denmark did so.