Twitter sued the US government Tuesday, claiming its free speech rights are being violated by restrictions on its ability to disclose numbers of secret orders to hand over user data.

The lawsuit filed in California steps up the battle between the tech sector and US authorities over how much information may be disclosed about vast electronic surveillance in the name of national security.

"It's our belief that we are entitled under the (US constitution's) First Amendment to respond to our users' concerns and to the statements of US government officials by providing information about the scope of US government surveillance -- including what types of legal process have not been received," Twitter vice president Benjamin Lee said in a blog post.

"We should be free to do this in a meaningful way, rather than in broad, inexact ranges."

Lee said the FBI and Justice Department have refused to allow Twitter to publish any specific numbers in its "transparency report" other than the ranges agreed upon with several other tech firms.

The accord with five major tech companies allows the publication of requests in a range such as zero to 999, or 1,000 to 1,999.

But Twitter, which was not among the five companies in the agreement, said it is not permitted to say whether it has not received any requests from the FBI or secret court.

- Bid for transparency failed -

The lawsuit says the US Justice Department and FBI have blocked efforts by Twitter to disclose specific numbers of FBI "national security letters" which require it to hand over user data, and orders from the secret Foreign Intelligence Surveillance Court.

"We've tried to achieve the level of transparency our users deserve without litigation, but to no avail," Lee said.

"In April, we provided a draft Transparency Report addendum to the US Department of Justice and the Federal Bureau of Investigation, a report which we hoped would provide meaningful transparency for our users. After many months of discussions, we were unable to convince them to allow us to publish even a redacted version of the report."

The lawsuit said the secrecy provisions are unconstitutional because they are "in violation of Twitter's right to speak about truthful matters of public concern."

The complaint argued that the public has a right to know about the extent of secret data requests or orders, in light of documents leaked by former National Security Agency contractor Edward Snowden.

"The Snowden disclosures have deepened public concern regarding the scope of governmental national security surveillance," the lawsuit said.

It added that Twitter "is a unique service built on trust and transparency" and that the inability to publish more detailed data hurts the messaging platform.

"Twitter is used by world leaders, political activists, journalists, and millions of other people to disseminate information and ideas, engage in public debate about matters of national and global concern, seek justice, and reveal government corruption and other wrongdoing," the lawsuit said.

"The ability of Twitter users to share information depends, in part, on their ability to do so without undue fear of government surveillance."

A Justice Department spokeswoman did not comment specifically on the lawsuit but said US officials stood by the compromise agreement reached in January.

"Earlier this year, the government addressed similar concerns raised in a lawsuit brought by several major tech companies," spokeswoman Emily Pierce said in an emailed statement.

"There, the parties worked collaboratively to allow tech companies to provide broad information government requests while also protecting national security."

The American Civil Liberties Union meanwhile praised Twitter for its action.

"Twitter is doing the right thing by challenging this tangled web of secrecy rules and gag orders," said ACLU deputy legal director Jameel Jaffer.

"We hope that other technology companies will now follow Twitter's lead. Technology companies have an obligation to protect their customers' sensitive information against overbroad government surveillance, and to be candid with their customers about how their information is being used and shared."

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