The U. S. government is likely to open a criminal investigation into the leaks of classified documents revealing a secrete surveillance program that monitored the telephone and email records of millions of Americans.On top of a slew of recent leaks that stoked controversy in Washington, it was revealed on Wednesday that the National Security Agency(NSA) is sweeping up data on telephone calls made by millions of Americans every day.Under orders from a top secret court, a copy of which was obtained by The Guardian, the NSA required Verizon, one of the largest telecommunications companies in the U. S., to hand over the telephone records of its customers on a daily basis.In addition, The Washington Post revealed on Thursday that the NSA and FBI are secretly gathering customer data from nine large U. S. internet companies, including Google, Facebook and Apple.The FBI and Justice Department are expected to open an investigation into the leaks, law enforcement and security officials said on Friday.Federal investigations into leaks typically begin after an agency files a complaint with the Justice Department after its secrets have been leaked without authorization.However, officials say that given the extent and sensitivity of the recent leaks, federal law may compel officials to open an investigation, whether the NSA files a complaint or not.U. S. President Barack Obama on Friday strongly defended the government’s vast data gathering program, describing it as a necessary tool to ward off terrorist attacks.“They help us prevent terrorist attacks, " the president said. That is worth the " modest encroachments on privacy, " he added.The U. S. government has been battling against national security leaks in recent weeks that involve intrusive government surveillance.In May, it was leaked that the Justice Department was involved in a massive and unprecedented search of the phone records of Associated Press journalists and a Fox News reporter.The Obama administration has prosecuted more people in cases involving leaking information than all previous presidents involved, according to The New York Times.