The US Consulate in Jerusalem and visiting Canadian officials were also targeted.
Israel’s Shin Bet security service says it has uncovered a plot to target Prime Minister Benjamin Netanyahu.
The Shin Bet says a resident of a Palestinian refugee camp in east Jerusalem is among those in custody for his involvement in the plot, orchestrated from Syria, to harm Mr Netanyahu and Jerusalem Mayor Nir Barkat.
It said on Tuesday that Mahmad Rashdeh had also collected intelligence on his Syrian handler’s behalf to target the US Consulate in Jerusalem and visiting Canadian officials.
It says the plan involved sneaking in an operative from Jordan and “significant terrorist activity” was foiled.
Mr Barkat said he was kept in the loop throughout the investigation and had not changed his routine at all.
He added that “no threat will deter us”.
There was no immediate comment from Mr Netanyahu’s office.