The son of the late al-Qaeda leader and 9/11 mastermind Osama bin Laden sent a letter to the US Embassy in Saudi Arabia to ask for his father's death certificate – a request that was refused by the diplomatic mission.

The revelation is contained in a stack of documents recently published by WikiLeaks, the whistleblowing organisation led by Julian Assange, who on 19 June marked the third anniversary of his political asylum in the Ecuadorian embassy in London.

In response to Abdullah bin Laden's request, the embassy wrote to inform him that no death certificate was issued for the terrorist leader. "This is consistent with regular practice for individuals killed in the course of military operations," reads the leaked document.

The letter is dated 9 September 2011, four months after bin Laden was killed by a US raid at his Pakistani shelter in Abbottabad. US officials said that bin Laden was buried at sea.

"There is another mechanism by which to certify the death of Osama bin Laden," reads the letter drafted by Glen Keiser, a consul general at the US embassy in Riyadh.

He refers to the nolle prosequi (Latin for "we shall no longer prosecute"), an order granted by the court that means the criminal case against bin Laden has been dropped and thus could act as proof of death.