Seven teenagers were arrested Tuesday night after they allegedly assaulted a woman and stole her cellphone on an Orange Line train, MBTA Transit Police said.

Transit Police officers met the woman at Tufts Medical Center Station, where she provided descriptions of the teens and told officers that the group had fled towards Tremont Street. Officers eventually caught up with the group at the intersection of Washington and Union Park streets in the South End, Transit Police said.

After confirming that the group matched the descriptions of the one given by the victim, officers arrested Kernisha Smith, 18, of Dorchester, Demario Barbara, 17, of Mattapan and four juveniles on charges of assault and battery with a dangerous weapon and unarmed robbery, police said.

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A seventh suspect, Eric Thompson, 18, of Dorchester, was arrested for the same charges after attempting to bail the group out at the Transit Police headquarters. An officer quickly realized Thompson was also involved with the attack, Transit Police said.

The victim’s phone was not recovered, said MBTA spokesman Joseph Pesaturo.

The suspects are expected to appear today in Boston Municipal Court or Boston Juvenile Court, police said.