Lebanon has only two or three days of fuel left and the United Nations is working urgently to persuade Israel to give safe passage to supply ships, UN officials said.
The lack of fuel and precarious security is preventing many UN organised convoys from reaching victims of the war in Lebanon which has left more than 820 dead in the past three weeks.
The United Nations estimates that at least 177 children have been killed in Lebanon while it also emphasised that children have also been killed in Hezbollah rocket attacks on Israel.
There is an "acute fuel crisis" in Lebanon with only two-three days of supplies left in the country. Three hospitals in southern Lebanon have closed because of the lack of fuel, he said.
"We hope that in the next 24 hours we will be able to resupply Lebanon with fuel. We are working with our colleagues in Jerusalem to get safe passage clearances (from Israel) for fuel ships to come to Beirut."
"The conditions are treacherous," said Ahmad Fawzi, a UN information service director.
"We are not getting security clearances for our convoys to go through," Fawzi told a press briefing at the UN headquarters. Only one food convoy to the south out of three planned was able to leave Beirut on Tuesday.
"The World Food Programme is increasingly frustrated at the decision of the IDF (Israeli Defence Forces) to allow only one of the three humanitarian convoys," Fawzi said.