Hamas on Tuesday denied that rockets were fired from Gaza into Israel on Monday evening, and accused Israel of looking for excuses to shirk its commitment under the cease-fire agreement to ease its blockade of Gaza. Hamas Prime Minister Ismail Haniyeh accused Israel of "backtracking on the calm." The IDF has said its sensor systems detected two rocket launches from Gaza on Monday. The actual impact sites have yet to be found and local security officials were still searching for them Tuesday morning. Following the attacks, Defense Minister Ehud Barak instructed the army to close the Gaza crossings on Tuesday. A military spokesman said only pedestrian traffic would be permitted for the time being. Palestinian officials said the closure meant that a long-awaited shipment of cement would not be allowed through on Tuesday. "The closing of the border today is unjustified and another indication that the Israeli occupation is maneuvering and trying to dodge the conditions of the calm understanding," Hamas spokesman Sami Abu Zuhri said. Abu Zuhri also accused the IDF on Tuesday of shooting a 65-year-old Palestinian woman who lives near the Israel-Gaza border in what he called "a grave violation of the calm understanding." The IDF said that a preliminary investigation indicated it was not involved. Meanwhile, Prime Minister Ehud Olmert declared Tuesday that nothing would stop Israel's "struggle to bring calm and security to the residents of the South." Speaking at a ceremony marking the opening of a new Intel factory in Kiryat Gat, Olmert said he would "continue negotiations to bring peace and create a new horizon of hope, and of development and prosperity all across Israel." Since the beginning of the cease-fire with Hamas, a number of mortar shells and Kassam rockets have been fired at Israel from the Gaza Strip. Monday's apparent Kassam attack came after a weekend during which a number of mortar shells were fired at southern Israel, including one which landed near Kibbutz Kfar Aza. Similar cease-fire violations earlier last week prompted Israel to close Gaza's cargo crossings, but on Sunday, the crossings were reopened to allow goods to be transferred into the territory. Also on Monday, Palestinian diplomat Nabil Amr said that Egypt would open the Rafah border crossing for two days to allow hundreds of stranded on both sides to cross.