The United Nations High Commissioner for Human Rights, Mary Robinson, and her delegation have been denied entry into Israel or Palestinian-ruled areas.
The Israeli government advised Robinson, who had planned to leave for the Middle East on Tuesday, to postpone her trip to the region until next week.
A UN spokesperson said the human rights mission would have to wait until the United States secretary of state, Colin Powell, has finished his Middle East tour, which is intended to secure a ceasefire between Israel and the Palestinians.
Robinson had planned to visit the region together with the former Spanish prime minister, Felipe Gonzalez, and the former secretary general of the African National Congress, Cyril Ramaphosa, in order to probe alleged human rights violations during Israel's military assault.
However, a statement issued after the three delegates had held talks in Geneva on Tuesday made it clear that they would have to wait for green light from Israel.
An envoy for the Jewish state informed them that Israeli officials were giving "careful consideration" to the request, but they were "bearing in mind other important impending visits".
Powell, who has visited Morocco and Egypt, will travel to Spain and then Jerusalem, where he is expected to meet the Palestinian leader, Yasser Arafat.
The International Committee of the Red Cross (ICRC) said they had been denied access to the West Bank town of Jenin, where heavy fighting between the Israeli army and Palestinian gunmen took place on Tuesday.
Vincent Lusser, a spokesman for the ICRC, said they were planning to send 12 vehicles to Jenin on Tuesday; however, the mission had to be abandoned for security reasons at the last minute.
The ICRC team in Jenin said they were negotiating with the Israeli authorities to allow Palestinian ambulances into the refugee camp to pick up wounded.
"It is impossible to even estimate the number of wounded as we have not had access to the camp yet. But we fear there are many wounded and sick," said ICRC spokeswoman Aleksandra Matijevic in Jenin.
According to Matijevic, only one UN ambulance was able to enter the camp and return to a hospital on Tuesday.
On Saturday, the ICRC said its humanitarian operations in the West Bank were at "a strict minimum" because of "totally unacceptable" threatening action by Israeli forces.
swissinfo with agencies