Terror attacks hit London

Amtrak police officer Richard Collins assists a passenger at Pennsylvania Station in Baltimore. Collins was called in on his day off to beef up security at the station.

Capitol Hill Police officer Scot Humphrey stands on guard in front of the Capitol building in Washington, D.C.

Police officers patrol at the Gare du Nord train station in Paris.

Trader Adam Heckendorn (center) watches the board as he works on the floor of the New York Stock Exchange.

Prince Charles talks to John Tulloch, one of those wounded in a bomb blast,at St.Mary's Hospital, London.

Members of the National Guard stand on high alert as they watch over New York's Penn Station in the wake of terrorist attacks on London's transportation system.

An Italian Carabiniere guards the front of the British Embassy in Rome. Italy raised its anti-terror alert and stepped up security after the series of attacks in London on Thursday.

Wreckage of the double-decker bus destroyed by a terrorist bomb remains in London street the day after the attack.

Following a series of explosions in London on Thursday, Chicago Police officers were stationed outside the Wrigley Building which houses the British Consulate-General.

Flowers and written sentiments sit next to the locked front gates of the British Embassy in Washington, D.C., following the London bombings Thursday.

A German police officer watches the entrance to the British Consulate in Munich Thursday.

Officer B. Hanna of the Washington Metro Special Response Team patrols the city's subway cars, Thursday.

A lone commuter waits to board a train on the Central Line during morning rush hour at Holborn underground station in London.

Spanish police check passengers at Atocha train station in Madrid after the London bombings on Thursday.

Amtrak police officer Lt. William Hurd patrols inside Pennsylvania Station in Baltimore. Security was beefed up at the station today following attacks on commuters in London.

London commuters ride a double-decker bus past the scene of a an attack on a similar bus outside Russell Square.

Maryland Transportation Authority Police examine an unattended vehicle at the departure ramp of Baltimore-Washington International Airport Thursday after the London attacks.

Douglas Stewart of Fairfax, Va., reads a paper Thursday under a sign that warns of heightened security at the Metro Center subway station in Washington, D.C.