British intelligence in 2015 caught an alleged Hezbollah terrorist stockpiling more than three tons of ammonium nitrate, a common ingredient in homemade bombs, on the outskirts of London, but never divulged the plot, The Daily Telegraph reported Sunday.

The report said the arrest came just months after the UK joined the US and other world powers in signing the Iran nuclear deal and speculated that it was hushed up to avoid derailing the agreement with Tehran, which is the main supporter of the Lebanese Hezbollah group.

Acting on a tip from a foreign intelligence agency, MI5 and the Metropolitan Police raided four properties in North West London, discovering thousands of disposable ice packs containing ammonium nitrate, the Telegraph said.

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A man in his forties was arrested on suspicion of plotting terrorism, but was eventually released without charges. The paper quoted “well placed sources” as saying that “the plot had been disrupted by a covert intelligence operation rather than seeking a prosecution.”

According to the report, the plot was part of a wider Hezbollah plan to lay the groundwork for future attacks and noted foiled Hezbollah operations in Thailand, Cyprus and New York. All those plots were made public and were believed to have targeted Israeli interests around the world.

The Telegraph said the Cyprus case was strikingly similar to the one in London. In 2015 in Cyprus, confessed Hezbollah agent Hussein Bassam Abdallah was sentenced to six years in jail after he was found with 8.2 tons of ammonia nitrate in his home. He had reportedly planned to attack Israeli targets.

The Telegraph said its information came after a three-month investigation in which more than 30 current and former officials in Britain, America and Cyprus were approached and court documents were obtained.

The Telegraph said that in Cyprus the ammonia nitrate was also stored in ice packs, saying that they were a convenient, seemingly harmless and easy to transport.

Sources told the Telegraph that the UK plot was at a very early stage and no targets had been selected. It said UK intelligence used to opportunity to try and establish what Hezbollah was up to and so did not disrupt it immediately.

“MI5 worked independently and closely with international partners to disrupt the threat of malign intent from Iran and its proxies in the UK,” a UK intelligence source told the paper.

“The Security Service and police work tirelessly to keep the public safe from a host of national security threats. Necessarily, their efforts and success will often go unseen,” said Minister of State for Security Ben Wallace.

But the Telegraph speculated that the incident was kept quiet because the US had just signed the Iran nuclear deal.

“It raises questions about whether senior UK government figures chose not to reveal the plot in part because they were invested in keeping the Iran nuclear deal afloat,” the paper said.

The US, under President Donald Trump, has since pulled out of the deal and hit Iran with fresh sanctions.

The paper also raised questions as to why the information was not revealed as the UK debated banning the entire Hezbollah organization earlier this year.

In March, it finally declared Hezbollah’s political wing illegal too after years of distinguishing it from its military wing.

Hezbollah was established in 1982 during the Lebanese civil war and fought a 2006 war with Israel. Its leader, Hassan Nasrallah, regularly threatens to target Israel with thousands of advanced missiles that can reach all major Israeli cities.

The group is considered a terror organization by Israel, the US and the Arab League. The European Union and Australia only designate the group’s military wing as such.

It has been blamed for a string of attacks against Israelis including the 2012 attack on a bus load of Israeli tourists in Bulgaria that killed five, the 1992 bombing of the Israeli embassy in Buenos Aires that killed 29, and the 1994 AMIA Jewish center bombing in Buenos Aires that killed 85 people and injured hundreds more.

Britain blacklisted Hezbollah’s military wing in 2008 but had until now made no move against its political wing.

However, British Foreign Secretary Jeremy Hunt said the UK now believes that any distinction between its military and political wings “does not exist.”

The move came after the group was included as part of Lebanon’s new government. While the cabinet is headed by Saad Hariri, a Western-backed Sunni politician who has held the job since 2016, Hezbollah made significant gains at the expense of the largest Sunni party and now controls three government ministries.

Tehran is a major supporter of Hezbollah and its “resistance” against the Islamic Republic’s arch foe, Israel.

During the debate, Labour, whose leader Jeremy Corbyn once referred to Hezbollah as his “friends,” said the Home Office had not provided evidence to justify its change in stance on the Iran-backed organization’s political wing.

“Decisions on the proscription of organizations as terror groups are supposed to be made on the advice of civil servants based on clear evidence that those organizations fall foul of the proscription criteria set out in legislation,” Labour said in a statement.