Meir Dagan, a former head of Israeli spy agency Mossad who worked to thwart Iran's nuclear programme while also opposing a military strike against it, died Thursday at 71, the government said.

Dagan, who battled liver cancer and had undergone a transplant, led the Mossad from 2002 through 2010.

He was reportedly tasked with sabotaging the nuclear programme of Israel's arch-foe Iran to prevent it from developing atomic weapons.

But while leading that secret war, he also strongly opposed a military strike against Iran, a position shared by the military's then-chief of staff Gabi Ashkenazi.

Prime Minister Benjamin Netanyahu and then defence minister Ehud Barak were reported to have given the order in 2010 for the military to prepare such a strike, which was never carried out.

In 2012, Dagan told US network CBS an Israeli attack would have "devastating" consequences for Israel and would be unlikely to put an end to the Iranian nuclear programme.

"An attack on Iran before you are exploring all other approaches is not the right way," Dagan said.

"And (President Barack Obama) said openly that the military option is on the table and he is not going to let Iran become a nuclear state, and from my experience, I usually trust the president of the US."

Under Dagan's leadership, the Mossad is believed to have assassinated Iranian nuclear scientists, caused explosions at nuclear facilities and used computer viruses to damage uranium centrifuges.

The Mossad has never confirmed such operations.

Several other controversial operations were attributed to the Mossad during Dagan's unusually long tenure, including a 2008 car bomb in Damascus that killed top Hezbollah operative Imad Mughniyeh.

Others included a 2008 air raid in Sudan against an alleged Iranian arms convoy said to be destined for Palestinian Islamist movement Hamas and a 2007 bombing of a suspected desert nuclear site in Syria.

The end of his tenure was marked by the 2010 murder of top Hamas militant Mahmud al-Mabhuh in a Dubai hotel.

The incident caused an international uproar, with the Dubai authorities quickly pointing the finger at Israel, and releasing surveillance footage showing a team of alleged Israeli agents they say killed Mabhuh.

There were reports that those involved used British, Irish, French, Australian and German passports.

In many cases, the travel documents appeared either to have been faked or obtained illegally. The countries whose passports were used all called in Israeli envoys for talks.

- 'A daring fighter' -

After leaving the Mossad, Dagan did not shy away from criticising Netanyahu.

He joined a protest in Tel Aviv in March 2015 against the prime minister in the run up to elections and delivered a fiery address.

"Israel has enemies but I do not fear them. What scares me is the current leadership of the country," he said.

Beyond Iran, his criticism of Netanyahu included his failure to advance peace efforts with the Palestinians.

The bespectacled and stocky Dagan was a descendant of Holocaust survivors who emigrated from Siberia to Israel in 1950.

He kept a photo hung in his office of his grandfather on his knees before being executed by Nazi soldiers.

Before taking the reins at the Mossad, he led a secret commando unit in the 1970s known as the Rimon squad, which reportedly carried out summary executions of Palestinians accused of attacks in the Gaza Strip.

He later served as an adviser both to Netanyahu and former prime minister Ariel Sharon.

Israeli politicians paid tribute to him on Thursday following his death, including Netanyahu, who called him "a daring fighter and commander who greatly contributed to the security of the state".

"Meir was determined to ensure that the Jewish people would never be helpless and defenceless again, and to this end he dedicated his life to building up the strength of the state of Israel," Netanyahu said in a statement.