US and British warplanes have begun an intense bombardment of Republican Guard bunkers outside Baghdad to prepare for a ground assault on the Iraqi capital.

Army helicopter gunships in the frontline of the attack were forced to turn back after encountering a hail of small-arms fire. One of the Army’s Apache helicopters went down. Shortly afterward, Iraqi state television showed the two crewmen, 26-year-old Chief Warrant Officer Ronald Young Jr, and 30-year-old Chief Warrant Officer David Williams.

The airmen were the second set of POWs displayed by the Iraqis.

Troops from the US army 5th Corps have formed a frontline about 50 miles south of Baghdad. Vast convoys of tanks and ground forces are racing up from Kuwait to join them. The US army’s 3rd Infantry Division is attempting to push towards Baghdad but is stalled by a sandstorm.

• May Ying Welsh, independent journalist in Baghdad.