A British teenager accused of planning a bombing in London has pleaded guilty to preparing terrorist acts.

Prosecutors say Haroon Syed tried to buy weapons and explosives online from an extremist named "Abu Yusuf." The contact was actually a series of British intelligence agents.

The 19-year-old told his contact he needed a machine gun and an explosive vest so he could "after some damage with machine gun do martyrdom."

He said he was considering targeting London's busy Oxford Street, and also searched online for potential locations, including an Elton John concert in Hyde Park on Sept. 11, 2016 — the 15th anniversary of the 9/11 attacks.

Syed was arrested Sept 8.

He pleaded guilty Thursday at London's Central Criminal Court. Judge Michael Topolski said he will be sentenced June 8.