cnn said the investigation started after intercepted communication and other intelligence information that led officials to believe that a plot could be under way.









the network quoted an official as saying the plot focused on parts of california and that officials there had stepped up security.









the transportation security administration had also alerted local law enforcement agencies responsible for security around airports in the state although the possible threat was not necessarily related to aviation, cnn said.









it added that some u.s. cities had increased their security, but gave no further details.









no one at the fbi was immediately available to comment. homeland security secretary jeh johnson also declined to comment on the reported threat to los angeles airport. 









 









 los angeles was already using two-man police patrols, but the continued isis call for sympathizers to attack western interests means upgraded measures at los angeles international airport.









 









 and while investigators say there is no specific plot to mention, intelligence from overseas and monitoring of suspected militants in the united states point to an increased threat. fbi director jim comey has said in recent weeks that there are investigations going on in all 50 states into alleged isis sympathizers.









 









 sources, speaking on a condition of anonymity to nbc, said fears revolve around uniformed personnel, such as police officers, or locations where "lone wolf" terrorists could target.









 









 "over the last few months, we have made a number of security adjustments, including enhanced screening at select overseas airports and increasing random searches of passengers and carry-on luggage on flights inbound to the u.s., reflecting an evolving threat picture," a department of homeland security spokesman said. 









 









 he would not comment on the specific intelligence that increased concerns on the west coast, but officials there have boosted security in recent months.









 









 more airport police have been placed on duty at los angeles international airport, reports the orange county register, in response to the threats. 









 









 "there are no specific threats to lax," insisted los angeles world airports, the airport oversight and operations department for the city of los angeles, in a press release. "we are constantly adjusting our deployment strategies, and as a precaution, have increased the visibility of airport police."









 









 the increased security also comes as counterterrorism experts worry that isis is growing in popularity in locations far away from syria and iraq, reports nbc. moreover,<u+00a0> violence continues to spread.









 









 in march, isis laid claim to an attack to the bardo museum in tunisia, with the violence escalating elsewhere since then.









 









 saudi arabia claimed isis was planning car bombings in riyadh after evidence was found on the cellphone of a man suspected of killing two police officers at a checkpoint.









 









 on monday, isis released a video showing the executions of ethiopian christians in two separate places in libya. isis also claimed responsibility for a suicide bombing in afghanistan that killed 34 people and wounded more than 100.









 









 in the united states, officials have been arresting people who want to travel to the isis caliphate in syria and iraq. in the past year alone, 39 u.s. citizens have been arrested for charges of offering to help isis, with eight americans arrested just in the last week.









 









 fordham center director karen greenberg said the appeal behind joining forces is the same for all potential isis recruits.









 









 "it's religion, but it's broader than just the religion itself. it's wanting to share in a culture in which that religion is central," greenberg said. "that is a place for them to go that will provide a religious homeland for them, and that they will be able to serve it in a number of capacities."









 










california airport security tightened amid isis fears
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