Gaza's border crossings will once again remain closed on Tuesday, following instructions by Defense Minister Ehud Barak. The decision came after the Gaza truce was breached yet again on Monday afternoon when a mortar shell was fired at the Karni crossing. The army said the shell landed in an open area near Nahal Oz, causing no casualties or damage. A high-level Hamas delegation is scheduled to arrive in Cairo Tuesday for talks with Egyptian government officials on the possibility of reaching a prisoner exchange agreement with Israel and to preserve the cease-fire in the Gaza Strip. The delegation will be headed by Musa Abu Marzouk, the Damascus-based deputy head of Hamas's political bureau, and Mahmoud Zahar, a senior Hamas official in the Gaza Strip. The visit comes amid reports of tensions between Hamas and Egypt over the continued closure of the Rafah border crossing. Hamas representatives were quoted over the past week as accusing the Egyptians of failing to fulfill their pledge to reopen the crossing after the implementation of the cease-fire agreement was reached between Hamas and Israel over two weeks ago. A top Hamas official said their representatives in Cairo would ask the Egyptians to reopen the border crossing at least three times a week to enable Palestinians to return to the Gaza Strip and leave for medical treatment. "This is the least we can expect from our Egyptian brothers at this stage," he said. "There is no justification for the continued closure of the Rafah border crossing in the wake of the truce." The official said that the lack of progress on the issue of the border crossings was behind the delay in achieving a breakthrough in the talks over the release of kidnapped St.-Sgt. Gilad Schalit. "The reopening of the Rafah border crossing would facilitate the release of Schalit," the Hamas official explained. According to reports in the Arab media, Hamas has asked the Egyptians to stop mediating in the case of Schalit. The reports claimed that Hamas was seeking European mediation instead. However, Hamas Prime Minister Ismail Haniyeh said Monday that his movement continues to regard Egypt as an honest broker. He said his government was constantly in touch with the Egyptians over the issue of the cease-fire and the situation in the Gaza Strip. He said that the Hamas delegation, which is expected to visit Cairo, would urge the Egyptians to reopen the Rafah border crossing. He added that the talks would also focus on efforts to achieve a prisoner exchange with Israel. According to Haniyeh, the Hamas delegation will seek clarification from the Egyptians regarding Israel's response to the list of Palestinian prisoners Hamas is demanding in return for Schalit. Haniyeh did not say how many prisoners Hamas was demanding. Some Hamas officials, however, have revealed that they presented the Egyptians with a list of 1,000 prisoners whom it wants released in three phases as part of a prisoner swap. Haniyeh reiterated Hamas's commitment to the cease-fire and called on all Palestinian factions to abide by it. But he accused Israel of violating the cease-fire several times in the past two weeks. "The Israeli breaches are an offense to the Egyptians, who worked hard to achieve the agreement," Haniyeh said. "The violations are aimed at maintaining the siege on the Palestinians and undermining Egypt's role as a powerful Arab country in the region."