The Israeli Supreme Court ordered the immediate expulsion of a Polish activist on Wednesday, due to his "connection with terrorist organisations."
Kamil Qandil, a Polish national whose father is a Palestinian Arab, is has been held in detention at the country's main international airport for over a week.
"Kamil Qandil should be immediately expelled from Israel because of his connection with terrorist organisations," Chief Justice Asher Grunis said, without elaborating.
Qandil's lawyer claimed that his client was not informed of the allegations against him during the hearing, part of which was held in the presence only of the judges and agents of Shin Bet, Israel's internal security service (also known as Shabak).
"I have done nothing which could have harmed the state of Israel," Qandil told the court.
Grunis responded that he was "perhaps not aware of his actions."
The Association of International Development Agencies (AIDA), an umbrella group representing more than 80 organisations, said Qandil was detained on arrival to work on a project to supply water to Palestinian Arabs in the south Hebron Hills in Judea, which is under full Israeli control.
"He said that the biggest losers would be the villagers of the south Hebron hills where the project is located and... the Polish taxpayers who fund it," a relative told AFP.
AIDA said in a statement on Tuesday that Qandil works for a group called Polish Humanitarian Action (PHA), and that he was holding a valid work permit issued by Israel when he was stopped and detained on September 2 at Ben Gurion airport near Tel Aviv on "security grounds."
It said PHA was seeking to refurbish rainwater cisterns on which Arab farmers depend for irrigation.
The Shin Bet, for its part, told Haaretz newspaper on Monday that Qandil was refused entry "due to security information that exists about him."
His deportation comes as a decision to uphold a ban on Kosher slaughter in Poland threatens to strain Israeli-Polish relations, which have traditionally been good.