The U.S military in Iraq says its troops killed five militants late Monday in Baghdad's Sadr City district.

A military statement said a U.S. Apache helicopter targeted gunmen carrying rocket-propelled grenade launchers, killing two of them.

In another incident, a group of soldiers shot and killed three militants in response to a roadside bomb attack on a U.S. military vehicle.

Violence has increased in Sadr City, a stronghold of the radical Shi'ite cleric Moqtada al-Sadr, since Prime Minister Nouri al-Maliki began an offensive against Shi'ite militias last month.

In a separate development, a jihadist Web site has released an audio recording of al-Qaida's second-in-command, Ayman al-Zawahiri, answering questions submitted to Internet forums.

In the two-and-a-half hour recording, Zawahiri said the jihad (holy war) in Iraq is most important.

Some information for this report was provided by AFP, AP and Reuters.