The popular street artist is believed to have visited Gaza in February, leaving behind four murals. One, depicting the Greek goddess Niobe, was drawn on a door, the last remnant of a two-storey house belonging to the Dardouna family in northern Gaza.

Unaware of its value, 33-year-old Rabie Dardouna said he was tricked into selling the door to an eager local artist for just 700 shekels. He now wants the door back.

The artist who bought the door, Belal Khaled, said he did not mean to trick anyone, adding he just wants to protect the painting and has no intention of profiting.

Banksy’s works have been valued up to hundreds of thousands of euro.

Mr Dardouna said he did not know who the British artist was but added: “I did not know that it was this valuable. I heard it can be sold for millions. Now I want the door back.”

Mr Khaled said: “I bought the painting to protect its artistic value and preserve it from damage. Another reason is to display it in other places as well. I don’t have any monetary interest in this.”

He said he has been in touch with Banksy’s representatives hoping to get a clearance to showcase the mural — titled Bomb Damage — in Gaza art exhibits.

The debate has heated up on Facebook with Palestinian activists and journalists accusing the buyer of tricking the Dardounas while others have defended him for buying it legally.

Mr Khaled agreed to show reporters the mural on condition that its location is not revealed.

The Dardouna home was one of 18,000 destroyed in the 50-day war between Israel and Gaza’s Hamas rulers last summer. Banksy is a critic of Israel and created works in Gaza and the West Bank to draw attention to the plight of the Palestinians.