Earlier in the day, Israel once again closed its cargo crossings, accusing Palestinian extremists of firing a rocket at southern Israel in violation of the shaky truce.

Gaza's Hamas rulers denied that a rocket had been fired Monday evening, and accused Israel of looking for excuses to shirk its commitment under the cease-fire agreement to ease its blockade of impoverished Gaza.

Extremists have attacked Israel at least three times since the June 19 truce. Israel has responded by closing its cargo crossings with Gaza, but has not responded militarily.

Olmert said Israel's restraint should not be misinterpreted as weakness.

"We are in favor of a genuine calm," he said while on a tour of southern Israel. "If it prevails, fine. If it doesn't, we know how to respond with full force, and in a manner that will guarantee complete security to the residents of the south."

The Israeli military said its radar detected a rocket from Gaza that struck near the communal farm of Mefalsim. But it said actual rocket fragments were not located.

Hamas spokesman Sami Abu Zuhri called the border closing "unjustified and another indication that the Israeli occupation is maneuvering and trying to dodge the conditions of the calm understanding." Gaza's Hamas prime minister, Ismail Haniyeh, accused Israel of "backtracking on the calm."

Abu Zuhri also accused the military yesterday of shooting a 65-year-old Palestinian woman who lives near the Israel-Gaza border. He called the shooting "a grave violation of the calm understanding." The military denied involvement.

Israel has taken a zero-tolerance approach to any violation of the cease-fire. Since the truce took effect, the crossings have been closed for five days because of rocket and mortar attacks. None of the attacks has caused serious injuries or damage.

In recent months, Israel's passages with Gaza have been sealed to everything but humanitarian aid and fuel supplies. Israel had committed under the truce to allow in larger shipments of some supplies, but because of the attacks, deliveries have not increased.

Egypt, too, sealed its border with Gaza after the Hamas takeover, opening it only occasionally on humanitarian grounds. Yesterday, Egypt again opened the Rafah crossing - Gaza's main gateway to the outside world - for two days to allow hundreds of people stranded on both sides to cross.

Palestinian diplomat Nabil Amr said Monday that Palestinians needing medical treatment and those with residency permits in Egypt or other countries abroad would be allowed into Egypt.

In January, Hamas blew up the border wall between Egypt and Gaza, allowing hundreds of thousands of people to move in and out of Egypt for nearly two weeks before it was resealed.