JERUSALEM — An Arab with Israeli citizenship and several West Bank Palestinians have been arrested on suspicion of carrying out the bus bombing in the heart of Tel Aviv on Wednesday, the Israeli police and the internal security service, the Shin Bet, announced on Thursday.

The bombing, which injured 21 people, was regarded as a terrorist act and was the first such attack to strike the Mediterranean city in more than six years. It revived traumatic memories of the second Palestinian uprising, rattling the population even as a cease-fire was in the works to end eight days of intense fighting between Israel and Hamas in Gaza.

A Shin Bet statement said that the suspects were rounded up within hours of the explosion. Most of them, it said, were from the Palestinian village of Beit Laqiya in the Ramallah area of the West Bank, and were associated with both Hamas an another militant group, Islamic Jihad. It said the suspects had recruited a resident of Taibe, an Arab village in northern Israel, who was originally from Beit Laqiya but who had become an Israeli citizen through a family unification program.