Six people were arrested in Greater London on Thursday as part of a possible terrorist plot "involving Islamist extremists, with potential UK targets," according to The BBC. Eight home and one business were searched and the six suspects — five men and one woman, between the ages of 18 and 30 — were taken into custody.

Police said the plot was not linked to the Summer Olympics, which begin just three weeks from tomorrow, but the city is understandably on edge with such a major international event on the horizon. The British government has prepared an unprecedented security operation — the biggest joint U.S.-U.K. operation since World War II — including tens of thousands of security guards, police, military troops, checkpoints, warships docked in the Thames River, and anti-aircraft missile batteries stationed around the city. 

Saturday is also the anniversary of the July 7 bombings that killed 52 people and injured hundreds more on city transportation back in 2005.

Adding to the atmosphere of uncertainty, in a separate incident on Thursday police closed the widely used M6 toll road after a suspicious incident aboard a passenger bus. Initial reports, again from BBC, said that man was seen pouring some kind of liquid into a bag or box that then began smoking, though that story does not appear to be confirmed. Aerial footage showed the motorcoach pulled over to the side of the road with passengers seated on the pavement surround by police crews, hazmat teams, and fire trucks. One witness who was stopped on the M6 said that he was told to stay in his car with the windows up and the air conditioning off. Police later said that it was not a "counter-terrorism" inicdent, but offered no other explanation for the road closure or heavy response. The road has since be reopened.

Image via Channel 4