The federal government submitted 1,745 applications in 2011 to a secret intelligence court to investigate -- mostly through wiretapping -- suspected cases of terrorism and espionage, a 10.5 percent increase over the year before, according to a Justice Department report released Friday.

The annual report said that 1,676 applications to the Foreign Intelligence Surveillance Court were solely for electronic surveillance. The rest asked permission to conduct physical searches or a combination of wiretapping and physical searches. The FISA court approved every surveillance warrant.

The federal government submitted 1,579 FISA applications in 2010, all but 68 of them for electronic surveillance.

"Unfortunately -- or rather, by design -- these statistics are opaque and any interpretation of their significance is speculative," Steven Aftergood, director of the Project on Secrecy at the Federation of American Scientists, said in an email to The Huffington Post. He noted that some investigations involved multiple authorizations, so it is difficult to gauge variations year to year. "These numbers don't tell us what kind of surveillance is going on or why -- just that there is a lot of it," he said.