LOS ANGELES (AP) -- Officials from Los Angeles to San Francisco reacted to a series of explosions at London transit systems by increasing security Thursday at train stations and airports, calling in bomb squads and establishing anti-terrorism command centers.
In Los Angeles, law enforcement officials said they have not received any information to believe the city was under any immediate threat but asked people to be aware of any suspicious activity.
''The uncertainty of what occurred in London is an uncertainty that will occur anywhere in the world when it comes to major metropolitan areas,'' Los Angeles County Sheriff Lee Baca said. ''It's a very unfortunate reality that we are into right now.''
Four blasts rocked the London subway and a packed bus during the morning rush hour. U.S. law enforcement officials said at least 40 people were killed and London hospitals reported more than 350 wounded in the terror attacks.
Los Angeles Mayor Antonio Villaraigosa said Los Angeles International Airport was on heightened alert. Police Chief William Bratton said his department had been contacted by Homeland Security and had been informed about an orange terror alert for mass transit.
The Los Angeles Police Department and the county Sheriff's Department established emergency command centers just after 4 a.m. Extra sheriff's deputies were sent to patrol Metrolink commuter stations and trains that serve about 3,700 people daily in the region.
The LAPD's bomb squad was mobilized in case any suspicious packages were found, and police officers were on modified tactical alert, meaning they couldn't end their shifts without permission, police Lt. Paul Vernon said.
In San Francisco, the Bay Area Transit System was significantly increasing security systemwide by adding police officers and closing bathrooms in all the stations, said Jim Allison, BART spokesman. The transportation system serves about 300,000 commuters daily in the region.
Allison said there was no reason to believe BART would be targeted and the measures were precautionary. Other security measures were not being made public, he said.
Gov. Arnold Schwarzenegger said the state has offered mutual aid support to counties and cities.
''During this time it is important that we all remain vigilant, aware and report any suspicious activity to law enforcement officials,'' he said in a prepared statement.
Villaraigosa expressed confidence in transit security and planned to be one of the 1.75 million people who ride buses and trains daily in the Los Angeles area.
''Today our hearts and prayers are with the people of London on a day when London should be celebrating their selection as host of the (2012) Olympic Games,'' Villaraigosa said. ''instead she stands in shock and sorrow.''