While widely expected, the decision was likely to trigger fresh international criticism of Israel. The government of Prime Minister Benjamin Netanyahu is already on the defensive over plans for expanding settlements in the West Bank and a growing Jewish presence in traditionally Arab areas of east Jerusalem, which Palestinians want to be the capital of their future state.
In addition, tensions over a holy site in Jerusalem's Old City have triggered street riots and played a role in deadly attacks that have left six Israelis dead in the last month.
The Foreign Ministry said the Geneva-based rights council's "obsessive hostility toward Israel" would make an impartial investigation impossible. Israel has long had a tense relationship with the council, accusing it of ignoring or downplaying rights violations emanating from the Palestinian side.
The main practical effect of Israel's decision to deny entry to the investigators is that they will be unable to travel to Gaza via the main Erez crossing, which Israel controls. It would be theoretically possible for the council's representatives to reach the coastal enclave via Egypt, but the Rafah crossing from the Egyptian side has been closed amid confrontations between Egyptian forces and Islamic militants operating in the northern Sinai Peninsula.
Egypt has also been demolishing homes along the border with Gaza to create a buffer zone and make it more difficult to construct tunnels running under the frontier.
Israel has generally brushed off criticism of its conduct in the Gaza war leveled by groups such as Amnesty International and Human Rights Watch, though it is conducting its own internal probe of several deadly episodes. More than 2,000 Palestinians were killed in the fighting in July and August, most of them civilians, but Israel faults Hamas for deliberately placing noncombatants in harm's way.
The militant group, which dominates Gaza, constructed tunnels, fired rockets and stored arms in densely populated civilian neighborhoods, drawing Israeli bombardment.
Seventy-two Israelis, all but six of them soldiers, were killed in the Gaza hostilities, during which Hamas and allied militant groups fired thousands of rockets and missiles into Israel. Large swaths of the coastal strip were devastated by the fighting, with reconstruction costs expected to be at least $4 billion.
Representatives of the U.N. commission embarked on their investigation in neighboring Jordan, where they began collecting evidence and testimony. U.S. Secretary of State John F. Kerry was to hold talks in Amman on Thursday aimed at calming regional tensions.
Sobelman is a special correspondent.