Syria’s national security chief is reportedly fighting for his life in a Damascus hospital under mysterious circumstances, after the deaths of a string of senior Syrian intelligence officials.

Kuwait’s Al-Siyasah newspaper suggests that Lt Gen Ali Mamlouk has been poisoned with cyanide while Al-Aan satellite TV reports that Mamlouk is receiving treatment for leukaemia.

Al-Aan, however, also cited sources that said the 69-year-old is under house arrest after the Syrian government learned of a phone call between him and Turkish intelligence officials shortly before Syrian political intelligence chief Rustom Ghazali’s death on 24 April.

Mamlouk would be the fourth Syrian intelligence official, suspected of being involved in former Lebanese Prime Minister Rafiq Hariri’s 2005 assassination, to die under mysterious circumstances.

After giving an unprecedented radio interview on 12 October 2005 about the assassination and denying his involvement, Ghazi Kanaan, Syria’s interior minister from 2004 to 2005 and head of Syria’s security network in Lebanon, reportedly shot himself in the head in his Damascus office.

In October 2013, news stories emerged that General Jameh Jameh, 59, a Syrian colonel in charge of the Syrian intelligence branch in Beirut at the time of the assassination, was shot dead by Syrian rebel fighters near his home in Deir Ezzor.

Then, on 24 April 2014, Syria’s former political intelligence chief, Rustom Ghazaleh, also thought to be involved in Hariri’s assassination, died in a Damascus hospital.

Ghazaleh’s death came just weeks after Syrian President Bashar al-Assad fired him and General Rafiq Shehadeh, head of military intelligence, after they quarrelled and Shehadeh and his associates apparently beat Ghazaleh up, according to a report in Lebanon’s Daily Star.

Ghazaleh had been seeking greater involvement in the battle against rebels in the southern province of Daraa, where he was born, AFP reported.

But Shehadeh "was categorically opposed to him taking part in the battle" in the area by regime forces backed by Lebanon's Shiite Hezbollah movement, a source told AFP.

At the time of his death Ghazaleh, 61, had been clinically dead in the hospital for several weeks following a severe head injury after the fight, Syrian Observatory for Human Rights Director Rami Abdul Rahman told the Associated Press.

A Kuwaiti newspaper is alleging that Mamlouk, now reportedly on his death bed, injected Ghazaleh with cyanide last week and killed him after the failure of a previous assassination attempt.