Israel will keep Gaza border crossings closed another day in response to Palestinian rocket fire that had violated a new cease-fire, the Defense Ministry said late Wednesday.

The decision came after Gaza's Hamas rulers said they would not police other militant groups that break the truce that went into effect last Thursday.

It was the first major hitch in the truce and raised questions about its ability to hold.

Islamic Jihad militants fired three rockets at Israel on Tuesday, saying they were retaliating for an Israeli raid in the West Bank, which is not part of the truce accord.

Israel responded by closing the border crossings just three days after it had stepped up shipments of vital supplies into Gaza, a key part of the truce accord. Hamas called that a truce violation.

The Israeli decision not to open the crossings Thursday was made in a high-level meeting, according to defense officials, speaking on condition of anonymity because the meeting was closed.

The officials said the tenor of discussions was to start the supply flow over every time the crossings have to be closed: waiting three days before increasing supplies, and another week before the next step, which might include more fuel shipments.

That would be a major setback for Hamas, with Israel holding out the threat that every time a Gaza militant fires a rocket or mortar, Israel would turn back the clock on supply flow. The main benefit of the truce for Hamas is the possibility of ending a yearlong Israeli blockade that has caused severe hardships for the already impoverished territory.

But Hamas sent mixed signals. Its officials were meeting with heads of smaller militant groups to persuade them to honor the truce, but in public statements, the group remained defiant.

Hamas leader Khalil al-Haya said, "Hamas is not going to be a police securing the border of the occupation (Israel). No one will enjoy a happy moment seeing Hamas holding a rifle in the face of a resistance fighter."