It said one of the drones had been intercepted by air defences Wednesday evening, in the fourth such drone attack in less than two months.

Experts say the use of such drones marks an escalation in attacks against American interests, by pro-Iranian forces using techniques deployed by Huthi rebels in Yemen against Tehran's regional rival Saudi Arabia.

Wednesday's attack was the first such attack on targets in the Iraqi capital, the Arab world's second-most populated city.

The Iraqi army said Thursday that it would give further details on the two drones which bypassed air defences at Baghdad airport, where troops from the US-led coalition against the Islamic State group are posted.

Earlier on Wednesday, five rockets had landed at Balad, an airbase further north where American contractors are based, a security source said.

They did not cause any casualties or damage, the source said.

The Balad base has been targeted so regularly that US weapons firm Lockheed Martin withdrew last month, citing concerns about the safety of its personnel.

Pro-Iran groups on Wednesday had hailed what they described as "one more victory" for the state-affiliated Hashed al-Shaabi paramilitary coalition, as commander Qassem Muslah was released.

Muslah had been arrested on May 26 by police intelligence on suspicion of ordering the killing of Ihab al-Wazni, a pro-democracy activist shot dead earlier that month by unidentified gunmen on motorbikes.

sbh/feb/par

LOCKHEED MARTIN