Three near-simultaneous blasts rocked the London Underground (subway) and one additional blast destroyed a double-decker bus in the city this morning, killing at least 37 and injuring more than 700 in a terrorist attack similar to the Madrid bombings of 2004. A previously-unknown group claiming affiliation with al-Qaeda has claimed responsibility for the bombings.

Only yesterday, London celebrated being awarded the 2012 Summer Olympics. Today the Group of 8 (G8) Summit, a major meeting of economically powerful nations, is getting underway in Scotland.

The U.S. Department of Homeland Security has raised the terrorism alert level for transit to ‘Orange’ or ‘High.’ This increased alert level only affects subways, light rail, regional rail, and intra-city bus routes. Officials are mainly concerned about systems in Washington, DC; Boston, MA; New York, NY; Miami, FL; and Chicago, Illinois, but stressed that they have not received any specific threats.