RISHON LEZION, Israel (Reuters) - Israeli police have arrested an Arab-Israeli lawmaker on suspicion of smuggling mobile phones for Palestinian security convicts in an Israeli jail, a police spokesman said on Friday.

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Basel Ghattas, a member of Israel’s parliament, or Knesset, was arrested late on Thursday and a magistrate’s court extended his detention by four days, the spokesman said.

“He is suspected of offences of conspiracy, fraud and breach of trust,” spokesman Micky Rosenfeld said.

Ghattas would not comment to reporters at the court on Friday. His lawyer Namir Idelby did not say whether the lawmaker denied or admitted any wrongdoing. He said there was no justification for keeping his client under arrest.

“This is clearly a political matter,” Idelby told reporters at the court.

Attorney-General Avichai Mandelblit said Ghattas was filmed by a police surveillance camera on Sunday handing four envelopes he had hidden in his coat to a Palestinian prisoner, jailed for 15 years for security offences, when he visited Ketziot prison in southern Israel.

“Immediately after, the prison guards searched the prisoner. The search revealed the four envelopes which contained 12 mobile phones, 16 SIM cards, two chargers and one earphone,” Mandelblit wrote in the letter to the Knesset speaker.

Ghattas initially denied he had smuggled in envelopes but after being shown the video he admitted that he had, and said he did not know that they contained phones, the letter - seen by Reuters - said.

Ghattas’s Ballad party is part of the Joint Arab List faction, a group of four Arab factions that holds 13 seats in the 120-member Knesset. Ballad members are particularly vocal in supporting Palestinian causes.

Ballad has often drawn anger from Israeli lawmakers who accuse its members of inciting violence and being disloyal to the state.

“Anyone who smuggles cellular phones for a jailed murderer understands full-well that their use could bring about further terrorist acts and murders and therefore poses a danger to the public,” Internal Security Minister Gilad Erdan said in a statement.

At least 231 Palestinians have been killed in violence in Israel, the occupied West Bank and the Gaza Strip since October 2015. Israel says at least 156 of them were assailants in lone attacks often targeting security forces and using rudimentary weapons including kitchen knives.

Others have been killed during clashes and protests.

Street assaults have killed at least 33 Israelis and two American tourists over the same period.