* Syria, Somalia most dangerous countries for journalists
* Rise in citizen journalism, crackdowns explain rise
PARIS, Dec 19 (Reuters) - More journalists were killed doing their job in 2012 than in any year since monitoring started 17 years ago, with Syria and Somalia seeing a particularly heavy toll, Reporters Without Borders (RSF) said on Wednesday.
Eighty-eight journalists were killed, a third more than last year, as security forces in various conflict zones cracked down on a new crop of citizen journalists attempting to document their activities, the Paris-based rights group said.
"The high number of journalists killed in 2012 is mainly due to the conflict in Syria, the chaos in Somalia and to violence by the Taliban in Pakistan," Christophe Deloire, the head of RSF, said in a statement.
Those responsible for mistreating or killing journalists, photographers and cameramen usually face no punishment, creating a sense of impunity which encourages further violence, he added.
In Syria, where rebels have been fighting forces loyal to President Bashar al-Assad since March 2011, reports by citizen journalists have partly filled a vacuum left by a lockdown on independent reporting.
Amateur footage from mobile phones of street battles, hospital scenes and devastation caused by bombing has provided fodder for new organisations trying to portray life on the ground.
"Without their action, the Syrian regime would be able to impose a total blockade on information in some regions and carry out its massacre with nobody watching," RSF said.
Sophisticated data surveillance allows governments to track who is publishing news online as well as their physical location. If threatened, citizen journalists often lack the means to seek safety outside their country.
While government forces are blamed for most attacks, Reporters Without Borders said rebels may be behind some executions in Syria, the deadliest place for journalists in 2012.
Seventeen professional journalists, notably Marie Colvin, a U.S. reporter for Britain's Sunday Times, 44 citizen journalists and four collaborators were killed there this year.
Somalia was the second most dangerous country for journalists, where 18 were killed, followed by Pakistan with 10 and Mexico with six deaths, mostly by organised criminals.