The US military told an al-Jazeera cameraman being held at Guantánamo Bay that he would be released as long as he agreed to spy on journalists at the Arabic news channel, according to documents seen by the Guardian.

The journalist has been in the prison without charge for three-and-a-half years after being accused by the US of being a terrorist, allegations he denies. He claims that he has been interrogated more than 100 times but not asked about alleged terrorist offences. Instead, Sami Muhyideen al-Hajj says US military personnel have alleged during interrogation that al-Jazeera has been infiltrated by al-Qaida and that one of its presenters is linked to Islamists.

Some of the interviews have been carried out by British interrogators, who also wanted the cameraman to spy for them. Mr Hajj was arrested in December 2001 on the Afghan-Pakistani border while on assignment. His allegations are contained in notes of visits he received in Guantánamo in June this year from his lawyer Clive Stafford-Smith. The notes have been declassified by the US military.

The documents appear to show that the American military views the broadcaster, which is popular in the Arab world and is about to launch an English language channel, as an al-Qaida front.

Mr Hajj said that in one session of questioning he was offered US citizenship if he became a spy: "They have said, 'If you work with us, we will teach you journalism, we will get you a visa to live anywhere you want, we will even give you US nationality, we will protect you, we will give you money. We will help you write a book and then we will publish it. This will help make the al-Qaida people contact you, and work with you.'"

Mr Hajj is a Sudanese national and is married with a five-year-old child. In the documents he also alleges that the US military threatened his family if he accepted release and then refused to spy on al-Jazeera. Al-Jazeera has angered the US by broadcasting recordings of Osama bin Laden threatening the west.

One of its correspondents is being held in Spain over alleged links to terrorism and at one point the US raised its threat level after wrongly believing terrorists were hiding coded messages in the scrolling text reporting the headlines that appears on the screen on al-Jazeera.

The US military has questioned Mr Hajj about one of al-Jazeera's presenters, Ahmad Mansour, who hosts an interview programme for the channel and used to work for the BBC. Mr Hajj says that he has been interviewed in Guantánamo by the British five times.

A Foreign Office spokesperson said: "Our position on torture and mistreatment is very clear. The British government is against mistreatment of any kind."