The death toll rose to four after two people died of their injuries.
The bomb went off yesterday inside the last bogey of a Cairo-bound train at Menouf station, a city in the Nile Delta, the Egyptian TV reported.
It was planted by unknown terrorists, it said.
The explosion took place after a policeman detected a suspected item in the bogey. He soon called his fellow security personnel who formed a cordon and evacuated the passengers from the train.
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Bomb disposal team and security forces rushed to the spot for investigations.
Official statement about the number of deaths was awaited.
In a separate incident, unknown militants attacked a police checkpoint in Al-Alamen road in North Coast area yesterday injuring three conscripts.