The UN says it has halted work on all but one of its 20 building projects in the Gaza Strip as a result of an Israeli ban on importing building materials into the Palestinian territory.
Israel imposed the ban after discovering on October 13 a 2.5km tunnel which it said fighters planned to use for attacks inside its territory.
Hamas, which has run the Gaza Strip since 2007, claimed it dug the tunnel.
"We are in now in the fourth week [in which] we are not allowed to bring in construction material," said Robert Turner, director of Gaza operations for the United Nations Relief and Works Agency (UNRWA).
"We do not know when we will be allowed to restart these projects."
UNRWA provides food aid to 830,000 of Gaza's 1.8 million population.
Turner called for the ban to be lifted, adding that the only building project still under way, a bridge, was also running out of building materials.
The others included 12 schools and a health centre. more