Iran was involved in bomb plots targeting Israeli diplomats in India, Thailand and Georgia in February, according to a media report.
In India, local agencies believed that a bomb attack which badly injured the wife of the Israeli military attache in New Delhi in February was the work of an Iranian 'security entity'.
Their conclusions have not previously been made public and Indian officials avoided blaming Tehran, an ally and a key oil supplier.
The governments of Georgia and Thailand, which both uncovered bomb plots on the day of the Delhi attack, have also not officially blamed Iran.
European intelligence officials said that they now found it difficult to judge Tehran's 'risk calculus'.
"Until recently it was possible to see why they were doing what they have been doing," The Guardian quoted an intelligence official as saying.
"Now it has become very unpredictable. It's very hard to see the logic behind [the February bombings], other than perhaps demonstrate an ability to cause problems in the event of war or a desire for revenge of some kind," the official added.
Police evidence, witness statements and court documents seen by the Guardian, plus interviews with local and international law enforcement and security officials, suggested that the attempted triple-bombing on February 13 and 14 was conducted by a well co-ordinated network of about a dozen Iranians and prepared over at least 10 months.
According to the paper, the evidence includes the identification of at least 10 Iranians allegedly involved in the plots, money transfers to key individuals from Iran, the use of Iranian phone connections and the flight following the attacks of conspirators to Iran.
Meanwhile, talks on Iran's nuclear aspirations will resume in Moscow on Monday, and western intelligence officials have warned that the price of failure could be high.
According to the paper, with Israel refusing to rule out military action if diplomacy fails, intelligence officials fear the volley of attacks carried out by Iranian operatives show Tehran is capable of an asymmetric response.