BASRA, Iraq — A rocket hit a site in southern Iraq used by foreign oil companies on Wednesday, including US energy giant ExxonMobil, wounding three people and threatening to further escalate US-Iran tensions in the region.

There was no immediate claim of responsibility for the attack near Iraq's southern city of Basra, the fourth time in a week that rockets have struck near US installations.

Three previous attacks on or near military bases housing US forces near Baghdad and Mosul caused no casualties or major damage. None of those incidents were claimed.

An Iraqi security source said it appeared that Iran-backed groups were behind the Basra incident.

"According to our sources, the team (that launched the rocket) is made up of more than one group and were well trained in missile launching," the security source said.

He said they had received a tip-off several days ago that the US consulate in Basra might be targeted but were taken by surprise when the rocket hit the oil site.

Iraq's military said three people were wounded in Wednesday's strike by a short-range Katyusha missile. It struck the Burjesia site, west of Basra, which is near the Zubair oilfield operated Italy's Eni SpA.

Police said the rocket landed 100 meters from the part of the site used as a residence and operations center by Exxon. Some 21 Exxon staff were evacuated by plane to Dubai, a security source said.

Exxon had evacuated its staff from Basra after a partial US Baghdad embassy evacuation in May and Exxon's staff had just begun to return.

Burjesia is also used as a residential and operations headquarters by Royal Dutch Shell PLC and Eni., according to Iraqi oil officials.

The oil officials said operations including exports from southern Iraq were not affected by the incident.

A separate Iraqi oil official who oversees foreign operations in the south said the other foreign oil firms had no plans to evacuate and would operate as normal.

A spokesman for Shell said its employees had "not been subject to the attack ... and we continue normal operations in Iraq." — Reuters