The son of Osama bin Laden has threatened revenge against the US for assassinating his father, according to an audio message posted online by Al-Qaeda.

Hamza bin Laden promised to continue the global militant group's fight against the United States and its allies in the 21-minute speech entitled "We Are All Osama," according to the SITE Intelligence Group, an organisation that tracks white supremacist and jihadi organisations online.

"We will continue striking you and targeting you in your country and abroad in response to your oppression of the people of Palestine, Afghanistan, Syria, Iraq, Yemen, Somalia and the rest of the Muslim lands that did not survive your oppression," Hamza said.

"As for the revenge by the Islamic nation for Sheikh Osama, may Allah have mercy on him, it is not revenge for Osama the person but it is revenge for those who defended Islam."

Osama bin Laden was killed at his Pakistani hideout by US commandos in 2011 in a major blow to the militant group which carried out the September 11 attacks.

Documents recovered from bin Laden's compound and published by the United States last year alleged that his aides tried to reunite the militant leader with Hamza, who had been held under house arrest in Iran.

The Bin Laden Tapes

Hamza, now in his mid-twenties, was at his father's side in Afghanistan before the 9/11 attacks and spent time with him in Pakistan after the US-led invasion pushed much of Al-Qaeda's senior leadership there, according to the think tank Brookings Institution.

Introduced by the organisation's new chief Ayman al-Zawahiri in an audio message last year, Hamza provides a younger voice for the group whose ageing leaders have struggled to inspire militants around the world galvanised by Isis.

In pictures: President Bush’s immediate response to 9/11 Show all 12 1 /12 In pictures: President Bush’s immediate response to 9/11 In pictures: President Bush’s immediate response to 9/11 11 September 2001 President Bush was visiting Emma E Brooker Elementary School in Sarasota, Florida as news of the attack on the World Trade Center broke In pictures: President Bush’s immediate response to 9/11 11 September 2001 The president and his staff, including Press Secretary Ari Fleischer (L) were then brought to a holding room at the school, where he prepared to address the nation In pictures: President Bush’s immediate response to 9/11 11 September 2001 President Bush was then rushed onto Air Force One and was flown to Barksdale Air Force Base in Louisiana. He watched television coverage of the attacks from his office on the plane In pictures: President Bush’s immediate response to 9/11 11 September 2001 President Bush talks on the telephone at the General Dougherty Conference Center at Barksdale Air Force Base In pictures: President Bush’s immediate response to 9/11 11 September 2001 President Bush is seen with his senior adviser Karl Rove at Barksdale Air Force Base In pictures: President Bush’s immediate response to 9/11 11 September 2001 The president with White House Chief of Staff Andrew Card at Barksdale Air Force Base. Before leaving the base, the president held a press conference at which he said, “Make no mistake: The United States will hunt down and punish those responsible for these cowardly acts” In pictures: President Bush’s immediate response to 9/11 11 September 2001 The president was consoled by Lt Col Cindy Wright of the White House Military Office aboard Air Force One. After leaving Louisiana, the president was flown to Offutt Air Force Base in Nebraska before he headed back to Washington In pictures: President Bush’s immediate response to 9/11 11 September 2001 President Bush arrived at the White House Presidential Emergency Operations Center around 7 pm. Here he is shown with his wife, First Lady Laura Bush, Vice President Cheney and National Security Adviser Condoleezza Rice In pictures: President Bush’s immediate response to 9/11 11 September 2001 At 8:30 pm, the president addressed the nation from the White House. In his speech, he set the tone for the wars to come in Afghanistan and Iraq In pictures: President Bush’s immediate response to 9/11 11 September 2001 “I’ve directed the full resources for our intelligence and law enforcement communities to find those responsible and bring them to justice,” the president said. “We will make no distinction between the terrorists who committed these acts and those who harbour them” In pictures: President Bush’s immediate response to 9/11 11 September 2001 The president’s speech on the teleprompter In pictures: President Bush’s immediate response to 9/11 11 September 2001 Immediately following the speech, the president had a national security meeting with Secretary of Defense Donald Rumsfeld, Vice President Dick Cheney, National Security Adviser Condoleezza Rice, White House Chief of Staff Andrew Card and others