UN Secretary General Ban Ki-moon said Tuesday he was "encouraged" by the release of Palestinian prisoners in exchange for Israeli soldier Gilad Shalit, who had been detained by Hamas for five years in the Gaza Strip. "The UN has been calling for the release of Gilad Shalit and all Palestinian prisoners," UN spokesman Martin Nesirky quoted Ban as saying. Ban was in Geneva and was on his way back to UN headquarters in New York. "He expressed his sincere hope that today''s release would have a far-reaching impact on the stalled Middle East peace process," Nesirky said. Ban recalled a September 23 statement by the UN, the European Union, the United States and Russia - the Quartet on the Middle East peace process - which called for the establishment of a Palestinian state living in peace next to Israel, and for Israel and the Palestinians to return to negotiations within four weeks from that date.