NEW YORK, United States — Civil rights lawyers sued the government yesterday to stop authorities from snooping in the laptops, cell phones and cameras of international travelers without probable cause.

The lawsuit was filed in US District Court in Brooklyn against the Department of Homeland Security as well as U.S. customs and immigration authorities. The government did not immediately return a message seeking comment.

The lawsuit says more than 6,500 people have had their electronic devices searched as they crossed US borders since October 2008. Nearly half of those searched were US citizens.

In May, a graduate student in Islamic Studies at McGill University in Montreal was detained for several hours as his electronic devices were searched, the suit says. The encounter badly frightened the student, according to the suit.

The American Civil Liberties Union, the New York Civil Liberties Union and the National Association of Criminal Defense Lawyers filed the lawsuit on behalf of the National Press Photographers Association, criminal defense lawyers and the student: Pascal Abidor, a 26-year-old French-American citizen whose laptop computer was confiscated at the Canadian border.

The civil rights groups said photographers regularly travel abroad with cameras, laptops and media storage devices to cover global news stories and rely on their ability to communicate confidentially with sources. They said many of the defense lawyers have similar confidentiality concerns as they travel abroad with laptops, blackberries and cell phones.

The lawsuit says policies adopted by US government agencies permit the search of all electronic devices that “contain information,” including laptops, cameras, mobile phones, ‘smart’ phones and data storage devices.

The policies are particularly invasive since electronic devices carry “vast amounts of personal and sensitive information that reveals a vivid picture of travelers’ personal and professional lives, including their intimate thoughts, private communications, expressive choices and privileged or confidential work product,” the lawsuit says.

ACLU staff attorney Melissa Goodman said the searches do not make people safer.

“Americans do not surrender their privacy and free speech rights when they travel abroad,” she said.

The lawsuit highlights what Abidor went through at the US-Canadian border as he traveled May 1 on an Amtrak train between Montreal and New York City to visit family after completing his academic year.

The lawsuit says a US Customs and Border Protection officer asked him a series of questions before he was asked to go with his belongings to the cafe car, where five or six other officers joined the questioning as he was ordered to provide access to his laptop.

The officer questioned him about some personal pictures and images of Hamas and Hezbollah rallies that he had downloaded as part of his research for his doctorate in the modern history of Shiites in Lebanon before he was searched, handcuffed and taken to a detention cell, the lawsuit says.

He was released after about three hours, leaving him “frightened, disturbed and severely upset” as he continued to New York on a bus, the lawsuit says.

The civil rights groups said that when Abidor’s laptop was returned 11 days later, there was evidence that many of his personal files, including research, photos and chats with his girlfriend, had been searched.

In a release, Abidor said: “This has had an extreme chilling effect on my work, studies and private life — now I will have to go to untenable lengths to assure that my academic sources remain confidential and my personal dignity is maintained when I travel.”

The lawsuit asks a judge to declare the policies unconstitutional and to stop them from being carried out when there is no reasonable suspicion.