A Spanish judge probing the alleged hacking of ministers' phones with Pegasus spyware has shelved his investigation over a "complete" lack of cooperation from Israel, a court statement said Monday.

In June 2022, Jose Luis Calama said he had sent a formal request for international judicial assistance, known as a letter rogatory, to the Israeli government asking for information about the software made by Israeli firm NSO Group.

He also said he wanted to go there in person to take a witness statement from NSO's chief executive.

But on Monday, the Audiencia Nacional, Spain's top criminal court, said Calama had decided to provisionally close the case "due to the complete lack of legal cooperation from Israel, which has not responded to the rogatory commission... and has prevented the investigation from going ahead".

The investigation began in May 2022 after the Spanish government said the spyware, which infiltrates mobile phones to extract data or activate a camera or microphone to spy on their owners, had been used against top politicians.

Among those targeted were the phones of Prime Minister Pedro Sanchez, Defence Minister Margarita Robles, Interior Minister Fernando Grande-Marlaska and Agriculture Minister Luis Planas.

But the Israeli government had never answered the request for assistance, which had been sent "four times", meaning "it probably never would", the court said in a statement, indicating the only remaining option was diplomacy.

"All that remains is a possible diplomatic channel capable of promoting compliance with the obligations derived from international treaties," it said.

The court said Sanchez's phone had been targeted on five occasions between October 2020 and December 2021.

But despite a prolonged analysis of the four phones, it had not been possible to determine "who was behind the attacks", the statement said.

Spain's government has blamed it on "an external attack" while the Spanish press has pointed the finger at Morocco given the context of an ongoing diplomatic crisis between the two countries at the time.

The scandal emerged in April 2022 when Canadian cybersecurity watchdog Citizen Lab published a report saying the phones of at least 65 Catalan separatists had been tapped following the failed 2017 independence bid.

Several weeks later, spy chief Paz Esteban told a parliamentary committee 18 Catalan separatists, including Catalan regional leader Pere Aragones, had been spied on with Pegasus software -- but always with court approval.