British intelligence seized tons of explosive materials linked to the Lebanese-based Hezbollah shi'ite organization outside London in 2015, the Daily Telegraph reported on Sunday.

The report reveals that MI5 and the Metropolitan police raided four properties in northwest London, uncovering three metric tons of ammonium nitrate and arresting a man on suspicion of plotting terrorism.

The Telegraph notes that the amount of ammonium nitrate found, a common ingredient in homemade bombs, was more than the amount used in the Oklahoma City bombings which left 168 dead.

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According to the report, a foreign government had warned Britain of the group's activity. “MI5 worked independently and closely with international partners to disrupt the threat of malign intent from Iran and its proxies in the U.K.,” an intelligence source told the paper.

Then-Prime Minister David Cameron and Home Secretary Theresa May were reportedly briefed personally on the event. The information was however kept secret.

A "well-placed source" told the Telegraph that the suspect arrested at the scene was released without charge due to the fact that the plot had "been disrupted by a covert intelligence operation rather than seeking a prosecution."

The report further speculates the incident was kept secret by the U.K. in order to keep the Iran nuclear deal afloat due to the fact that Tehran is a major supporter of the Lebanese Shi'ite group.

In February, Britain looked to classify Hezbollah's political wing as a terror group. Although its military wing was outlawed respectively in 2001 and 2008, the U.K. said it was looking to add the group in its entirety to a list of banned terror organizations. The U.S., Israel and the Arab league also consider the group a terror organization.