The Holy City is on edge following a series of deadly "lone-wolf" attacks on Israelis, including deliberate hit-and-run incidents by Palestinian drivers, and the killing of five people in a synagogue.
The 30 suspects, members of a West Bank-based network, were detained in September, domestic security service Shin Bet said after lifting a gag order on the operation.
Aged 23 to 30, they were recruited from Jordan, the West Bank, the Gaza Strip and Syria, by Hamas commanders based in Turkey, Shin Bet said.
Jerusalem's light railway, which links Jewish settlements in annexed Arab east Jerusalem to the city centre, was also on a list of potential targets, Shin Bet said.
No details were given on the types of attacks planned, or the fate of the suspects.
But the attacks would have claimed "many victims," Prime Minister Benjamin Netanyahu said in a statement.
There was no immediate response from Hamas, which controls the Gaza Strip.
Turkey, whose relations with Israel have soured in recent years, fiercely condemned Israel's bombardment of the tiny coastal territory in July and August that killed nearly 2,200 Palestinians.
Any deal was put off indefinitely by Israel's Gaza operation.
