CAIRO (AFP) - A bomb blast just 100 metres from a Cairo presidential palace wounded a female passer-by early Thursday, just hours after a train bomb killed three people, security officials said.

The new bombing followed an attack on a train north of the Egyptian capital late on Wednesday which killed two policemen and a civilian, the latest in a spate of attacks since the army ousted Islamist president Mohamed Morsi in July last year.

The blast struck near a palace in the northeast of Cairo which is rarely used by President Abdel Fattah al-Sisi, the architect of Morsi's overthrow, whose main office is in another palace in the capital.

The bystander suffered only minor injuries from the crude bomb, which was planted under a bridge, interior ministry spokesman Hani Abdel Latif told AFP.

Wednesday evening's train bomb in Menufiya province was also rudimentary but it detonated as police were inspecting it, killing two officers and one passenger.