For the past three months, a 23-year-old Israeli journalist has been under a secret house arrest over charges that she leaked classified information suggesting that the Israel military violated a legal ruling on killings of militants in the West Bank.

An unusual gagging order preventing reporting of the case by the media in Israel will be challenged next month by Channel Ten TV and the newspaper Haaretz.

The charges against Anat Kam, which could carry a heavy prison sentence if she is convicted, are believed to accuse her of photocopying classified documents during her period of military service.

Although the charges are not thought to specify a particular media outlet or article, there has been speculation that they relate to an investigation by the journalist Uri Blau in Haaretz magazine in November 2008. That report suggested that one of two Islamic Jihad militants killed in Jenin in June 2007 had been targeted for assassination in apparent violation of a ruling issued six months earlier by Israel's supreme court.

While not outlawing assassinations in the West Bank altogether, the ruling heavily restricted the circumstances in which they were permissible, effectively saying that they should not take place if arrest was possible.

Mr Blau's article said that the assassination of one of the militants killed in Jenin, Ziad Malaisha, had been approved in advance by officers, provided his car did not contain "more than one identified passenger". At the time of the shootings the military said it had killed Malaisha and another militant after they opened fire at a joint army and border police patrol.

Ms Kam was arrested more than a year after Mr Blau's report was published. At the time of her arrest, she was working for the news service Walla, which until recently was owned by Haaretz.

Discussions between the defence and the prosecution are under way and likely to be completed next week after the Passover holiday. A date for Ms Kam's trial has reportedly been fixed for 14 April, with the legal challenge to the gag order scheduled two days earlier in Tel Aviv district court.

The Israeli military declined to comment on the case yesterday.

One of Ms Kam's lawyers, Eitan Lehman, yesterday declined to discuss details of the case because of what he said was a warrant prohibiting publication. He said that leaks about the case had come from "the other side and not from us", including police sources. He added: "We are doing our best to abide by the terms of the warrant and to obey the law."

According to the Jewish Telegraphic Agency (JTA), a long-established US-based news service which serves the Jewish diaspora, the November 2008 report in Haaretz was approved by Israel's military censor. The news agency said that the charges against Ms Kam – which she denies – were under Israel's espionage and treason laws.

JTA quoted Dov Alfon, editor-in-chief of Haaretz, as saying it was "absurd" to link Ms Kam's arrest and the 2008 article. JTA said Mr Alfon had implied that Mr Blau had obtained his information without Ms Kam's help.

Mr Alfon was quoted as adding: "Haaretz asked the court to lift the gag order, not just in the public interest but also to allow us to defend ourselves from this absurd allegation. More than a year passed between the publication and her arrest, a year in which Uri Blau published several other front-page articles criticising the army's conduct."