Israel's Shin Bet security service says it has uncovered an alleged plot to target Prime Minister Benjamin Netanyahu.
The domestic intelligence agency said 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 Muhammad Rashdeh, a 30-year-old Palestinian from Shuafat refugee camp, had also collected intelligence on his Syrian handler's behalf to target the US Consulate in Jerusalem and visiting Canadian officials who were to train Palestinian Authority security forces in the West Bank.
It said the plan involved sneaking in an operative from Jordan, and "significant terrorist activity" was foiled.
He was arrested on April 24. Two other suspects were arrested but the Shin Bet did not identify them.
Mr Barkat said he was kept in the loop throughout the investigation and had not changed his routine at all. He said: "No threat will deter us."
There was no immediate comment from Mr Netanyahu.
Rashdeh received his orders from the Popular Front for the Liberation of Palestine - General Command (PFLP), the security service said. The Syria-based group supports Syrian President Bashar Al Assad.
The group, a splinter of the PFLP, carried out militant attacks in Israel in the 1970s and 1980s.
The Israeli prime minister is not the only high-profile politician in the country to be the target of an assassination plot.
In 2014, Israel arrested four Palestinians over an alleged plot to kill Israel's current defence minister Avigdor Lieberman with a rocket-propelled grenade. Mr Lieberman is one of the Israeli cabinet's most far-right members. Israel blamed Hamas, the rulers of Gaza, for the plot.
At the time, he was the country's foreign minister, and was the only serving foreign minister to live outside of his own country. He resides in a West Bank settlement, which much of the international community deems to be illegal.
The men planned to fire the RPG at his vehicle as he left the settlement of Nokdim.