The subway train that plowed into another, causing a crash that killed seven and injured scores of others in Washington, was part of an aging fleet that federal regulators had recommended three years ago be phased out or retrofitted, a safety investigator said today.

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Debbie Hersman of the National Transportation Safety Board said the Metrorail transit system "was not able to do what we asked them to do."

The rush-hour crashed sent more than 70 people to area hospitals and killed at least seven people. The three-decades-old Metro system shuttled tourists and local commuters from Washington to Maryland and Virginia suburbs.

There was conflicting information about the number of fatalities.

Mayor Adrian Fenty announced Tuesday that seven had died in the crash along a part of Metro system track that carries passengers from the District of Columbia into suburban Maryland. The District of Columbia Fire Department Web site announced early Tuesday morning that three bodies had been found in addition to the six fatalities reported earlier.

Fenty said two victims were hospitalised in critical condition.

Hersman said investigators expect to recover recorders from the train was struck, providing valuable information that might help determine why the crash occurred. However, the train triggered the collision was part of an old "thousand-series" fleet that was not equipped with the devices, she said at a news conference.