The United Nations and other international agencies on Tuesday called on Israel to allow construction material into the Hamas-controlled Gaza Strip to rebuild schools destroyed in bombings, according to dpa. Israel has imposed a tight blockade on the Gaza Strip after the radical Hamas movement seized control of the enclave in June 2007. According to the UN, during a 22-day Israeli military offensive on the Gaza Strip that ended on January 18, at least 280 schools were damaged, including 18 that were completely destroyed. The UN said none of the schools have been rebuilt due to the lack of construction material. The Israeli blockade has also caused shortages in textbooks, uniforms and stationery in Gaza. Philippe Lazzarini, an acting UN humanitarian coordinator, said the Israeli blockade "has caused countless suffering to children in Gaza, who face another academic year in terrible conditions." "The blockade threatens the basic rights of children and threatens to ruin the shining success achieved in the field of education," said Sigrid Kaag, Unicef regional director. Israel has refused to open the Gaza commercial crossings as long as Hamas keeps in its captivity Israeli soldier Gilad Shalit, who was abducted in June 2006.