The Israeli Navy stopped a Free Gaza boat from reaching the Gaza Strip Monday overnight, activists said. One person on the boat said the navy threatened passengers that they would be shot at if they did not turn back. The 21 human rights and solidarity workers, representing eleven different countries, set sail from Cyprus Monday morning for Gaza in yet another attempt to break the Israeli blockade of the Palestinian territory. The small ferry "Spirit of Humanity" is carrying three tons of medical aid, children's toys, and rehabilitation and reconstruction kits for 20 family homes. Passengers on board include former US congresswoman Cynthia McKinney and Nobel Peace Prize laureate Mairead Corrigan Maquire. Free Gaza Group organizer Ramzi Kysia said that each passenger was also carrying a kilogram of cement, an olive tree sapling, a water purifier, school materials and construction tools, in a gesture of solidarity with Gaza's 1.4 million people. "Gaza doesn't need charity, it needs the siege to be lifted," Kysia said. On Thursday, Cyprus' Merchant Shipping Department prevented the international activists from sailing to the Strip to deliver humanitarian aid. Department chief Sergios Sergiou said that a fishing boat and a small ferry that the Free Gaza Group were to use for the trip from Cyprus to Gaza had not undergone safety inspections which would take "at least a few days" to complete. The Free Gaza Group has already made five successful boat trips from Cyprus to Gaza since August 2008. Kysia said the fishing boat sailed to the Palestinian territory in August last year. The ferry set sail in January this year during Israel's Operation Cast Lead in Gaza, but had to turn back a few hours into the trip after encountering mechanical problems. Sergiou could not explain why the vessels were previously allowed to leave Cyprus. Israel launched the blockade on the Gaza Strip in response to persistent Palestinian rocket attacks against Israeli communities in the western Negev. Despite the general closure, Israel has consistently allowed trucks carrying essential supplies and humanitarian aid to flow through the border with Gaza.