"Wheat supplies scheduled to arrive in Gaza on the 9-10 December were unable to enter due to rocket fire, hence the mills have run out of flour and UNRWA has been forced to suspend food distribution," the agency said in a statement.
"Food distribution for both emergency and regular programs will be suspended from Thursday 18th December until further notice."
On average, the agency distributes food to about 20,000 Palestinians every day.
Al Jazeera's Sherine Tadros, reporting from outside a distribution centre in Gaza City, said dozens of people had been turned away since the agency's operations were halted.
Tensions along the border between Gaza and Israel have increased as a six-month truce, which both sides accuse the other of repeatedly violating, has approached its end.
On Wednesday, a Palestinian man was killed and two others injured in an Israeli air raid on the town of Beit Lahiya on Wednesday, Gazan medics have said.
An Israeli army spokeswoman the raid was aimed at rocket-firing squads and was launched in response to earlier attacks on the city of Sderot in southern Israel.
Gazan witnesses told the AFP news agency that 47-year-old Falak Okel, who died in the attack, did not belong to any armed group.
The Israeli spokeswoman said fighters in Gaza had fired at least 20 rockets at Sderot, and that two people had been injured by a homemade missile which hit a shopping centre car park.
Israel has sought to extend the Egyptian-brokered truce but Hamas, which has had total control of Gaza since June 2007, suggested it would not renew the ceasefire until Israel lifts its blockade.
"The Hamas position is not for the extension of the truce," Fawzi Barhoum, a Hamas official, said.
"The one who called for the truce and did not commit to it and worked towards its collapse is the Zionist occupation."
However, ordinary citizens from both sides appear to favour an extension with an opinion poll on Tuesday indicating that 74 per cent of Palestinians and 51 per cent of Israelis backed the truce.