A leading Israeli Arab politician, Azmi Bishara, is being investigated for allegedly helping Hezbollah during last year's conflict in Lebanon.
Bishara, a critic of Israeli policies, says he is being persecuted
This emerged after an Israeli court partially lifted a blackout on news about the case.
Mr Bishara resigned from the Israeli parliament earlier this month after leaving the country. At the time the allegations against him were not known.
He says he is being persecuted for criticising Israel's politics.
Mr Bishara has caused controversy in Israel before because of visits to Lebanon and Syria.
'Aiding the enemy'
He is under suspicion of crimes against Israel's security, aiding the enemy during war, contacting foreign agents and receiving money from abroad in violation of anti-money-laundering laws, police spokesman Micky Rosenfeld is quoted by the Associated Press as saying.
Some of the alleged offences were carried out during Israel's war against Lebanon over the summer, Mr Rosenfeld said.
Mr Bishara tendered his resignation at the Israeli embassy in the Egyptian capital, Cairo, saying he would stay abroad for a while.
He has always been an outspoken critic of policies toward the Palestinians, and leads the National Democratic Assembly (Balad), which has three members in the 120-seat Knesset.
He entered parliament in 1996 and three years later became the first Arab Israeli to run for prime minister. He is a Christian and resident of the northern Israeli town of Nazareth.