Police questioned an Arab Israeli lawmaker Tuesday over accusations he smuggled mobile phones to Palestinian prisoners, allegations prompting right-wing politicians to call for his removal from parliament.
Basel Ghattas of the Joint List, a coalition of Arab Israeli parties, has denied the accusations.
Israeli police from a major crimes unit questioned Ghattas "on suspicions of fraud, breach of (public) trust and entering objects into a prison", they said in a statement.
"The suspicions are that he illegally smuggled phones and SIM cards to security prisoners serving in prison. The investigation is continuing."
Police declined to provide further information. Members of the 60-year-old's Balad party said he was questioned for four hours in Lod, a city near Tel Aviv.
In response to the accusations a committee of the Knesset, Israel's parliament, decided on Thursday to restrict future visits to "security prisoners" by MPs.
A Knesset statement said the clampdown was requested by Public Security Minister Gilad Erdan on the advice of the Shin Bet security service.
Yoav Kish, chairman of the Knesset House Committee, said in remarks broadcast on public radio that a number of MPs from both the government and the opposition would be authorised to make visits "in order to ensure proper parliamentary oversight of prisoners' conditions."
One of the prisoners is serving time over the kidnapping and murder of an Israeli soldier in 1984, news site Ynet reported.
'Traitors and spies'
Ghattas had visited the Ketziot jail in the Negev desert in southern Israel.
Arab lawmakers from the Joint List, the third largest force in parliament with 13 seats, frequently clash with Israel's leaders.
Arab Israelis make up some 17.5 percent of the country's population.
They are the descendants of Palestinians who remained on their land after the creation of Israel in 1948.
They hold Israeli citizenship, but largely see themselves as Palestinians.
Prime Minister Benjamin Netanyahu said Ghattas should be "severely punished" if the accusations are proven.
Defence Minister Avigdor Lieberman said "this is extra proof that the Joint List is in fact a unified list of traitors and spies".
Balad is especially critical of Israeli policies and one of its members of parliament, Haneen Zoabi, has frequently angered Israeli officials.
The party has denounced the investigation as a further attempt to smear it.
Balad's three parliamentarians triggered outrage among Jewish Israelis earlier this year when they met relatives of Palestinians who authorities say were killed while carrying out attacks.
In response, parliament passed a controversial law in July allowing the expulsion of lawmakers deemed guilty of racial incitement or supporting armed struggle against Israel.
Some right-wingers have called for Ghattas to be expelled from parliament, but centrist and left-wing lawmakers say the investigation must be allowed to play out.
Many analysts have said the law will be extremely difficult to put into practice as any expulsion would require the support of 90 of the 120 lawmakers.