BOSTON (AP) - The head of the Massachusetts Bay Transportation Authority is promising an independent review of recent derailments on the Boston-area transit system.

MBTA General Manager Steve Poftak called for the "third-party assessment" after a subway derailment Tuesday morning at the above-ground JFK/UMass stop.

Poftak says officials are investigating why the third car of the Red Line train went off the tracks, resulting in "significant damage" to the vehicle, the tracks and signals.

No serious injuries were reported, but the incident caused widespread disruption for riders, which was expected to continue during the afternoon commute.

Nine people were sent to hospitals Saturday after a Green Line train derailed near Kenmore Square.

Poftak says there is no connection between the two incidents. Officials blamed the weekend incident on operator error.

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