U.K. Prime Minister Theresa May was the target of an assassination attempt by Islamist militants that was broken up last week with the arrests of two men, Sky News reported. 

Police believe the plotters planned to detonate an improvised explosive device at the prime minister’s Downing Street offices and kill May in the chaos, Sky reported, citing people it didn’t identify. Andrew Parker, director general of the MI5 security service, briefed cabinet ministers on the plot, Sky said.  

A weeks-long investigation into the case culminated last week with the arrests of two men on charges of preparing acts of terrorism, according to the report.

Naa’imur Zakariyah Rahman, 20, from north London and Mohammed Aqib Imran, 21, from southeast Birmingham were due to appear at Westminster Magistrates’ Court on Wednesday morning, Sky reported.

Parker told ministers that U.K. authorities had broken up nine potential terrorist attacks over the past year. But others have been successful. An official report released Tuesday on a suicide bombing that killed 22 people at the Manchester Arena in May found that opportunities to thwart the attack had been missed.