Two senior Arab-Israeli activists have been arrested on charges of espionage and contacts with Hizbollah.
Their arrests, which took place over the past three weeks, were the subject of a gag-order until it was partially lifted on Monday.
Amir Mahoul, 52, of Haifa and Omar Said, 50, of Kfar Kana are currently being questioned by the General Security Service (the Shabak) and the police's International Investigations Unit.
The two were arrested on charges of serious espionage and contact with a foreign agent who was, according to the Shabak, a member of Hizbollah.
Mr Mahoul, a veteran political activist and the head of two organisations dedicated to Arab civilians' rights, is the brother of former Knesset member Issam Mahoul. The siblings are founding members of the Balad party, as is Mr Said, who was in the past forbidden by the police from travelling abroad due to previous investigations.
The party condemned the arrests, saying that they were a continuation of the political persecution of Israeli Arabs in general and of the party's members in particular.
They claimed that the government is trying to cut off their community's ties with the Arab world.
Mr Said was arrested three weeks ago but the story began appearing on websites and blogs last weekend following the early morning arrest of Mr Mahoul at his home in Haifa.
The reports on the internet rendered the gag-order ineffective and large numbers of Israeli Arabs and left-wing activists took to the streets of Haifa to protest the secret arrests.
On Monday, the Shabak requested that court partially remove the gag order it had taken out and made the arrests public.
On Wednesday, the court extended their arrest by five days.
Security sources say that Hizbollah and its Iranian backers have been making significant efforts to recruit Israeli Arabs as agents.
Last month a 23-year-old from Kfar Kassem was convicted of supplying information to Hizbollah on the movements of the IDF's Chief of Staff, Lieutenant General Gabi Ashkenazi.
He was sentenced to five and a half years in prison.