FACTBOX: Security steps for Beijing's Olympics

(Reuters) - China, which says it has already cracked domestic terror plots targeting the Olympics, has taken sweeping steps to secure the Games against protests or attacks.

Here are some facts about security at the Games which open on Friday.

SCREENING VISITORS, LOCALS

-- Visa rules have tightened. Travelers must now show a return air ticket and a hotel booking before buying a visa.

-- Hong Kong, host of equestrian events, has created a watchlist of unwelcome activists and brought in new visa restrictions.

-- Interpol is to give Beijing airport and other major border entry points access to its database of more than 14 million lost or stolen travel documents.

-- Many Beijing dissidents and their families are being held under house arrest. Petitioners who have come to the capital to present complaints have often been detained, they said.

SECURITY CAPABILITIES

-- A 100,000-strong security force, including the elite Snow Wolf Commando Unit, is on alert.

-- 300,000 surveillance cameras watch the city.

-- Since May, the team of People's Liberation Army (PLA) engineers in charge of Games security checks and emergency rescues has run daily drills on finding and defusing explosives and rescuing and evacuating people from damaged buildings.

-- The U.N. nuclear watchdog has trained Chinese security personnel in how to respond to radiological attacks -- such as a "dirty bomb" -- in which radioactive material is released.

OLYMPIC VENUES

-- At least two surface-to-air missile launchers were set up in late June south of the Bird's Nest National Stadium.

-- Authorities pledged to revamp public emergency shelters by the venues last October, saying 20 to 30 new shelters, with room for 1.5 million to 2 million people, were needed every year.

-- Gas stations within 300 meters of Olympic venues and all Games-designated gas stations must install video surveillance equipment and "explosion-prevention devices".