In a statement released on Monday, the organisation called the blockade "collective punishment", a crime under international law. It described Gaza as a territory plagued by frequent power cuts, a ruined economy, and a collapsed health care system.
"The closure imposed on the Gaza Strip is about to enter its fourth year, choking off any real possibility of economic development," the ICRC said.
"Gazans continue to suffer from unemployment, poverty and warfare, while the quality of Gaza's health care system has reached an all-time low."
Israeli officials insist that they provide enough "humanitarian aid" to cover Gaza's basic needs.
But the ICRC said the meagre list of goods allowed into Gaza doesn't meet the needs of the territory's 1.5 million inhabitants.
Beatrice Megevand-Roggo, the head of the ICRC's Middle East operations, told Al Jazeera that the organisation - which traditionally remains neutral - was reluctant to publicly criticise the blockade. But she said three years of quiet efforts to ease the embargo did not result in any progress.
"The result has not been what we expected, and we thought that after three years the situation was dire enough, serious enough, to speak out publicly to try to break this closure of Gaza," she said.
The shortages are particularly dire in Gaza's health care system, where the ICRC said more than 100 essential medicines - including chemotherapy and hemophilia drugs - are unavailable. Many basic medical supplies, like colonoscopy bags, are also barred from Gaza and routine blackouts cause damage to medical equipment.
"The state of the health-care system in Gaza has never been worse," Eileen Daly, the ICRC's health co-ordinator in Gaza, said.
"Thousands of patients could go without treatment, and the long-term outlook will be increasingly worrisome."
'Unacceptable and counterproductive'
In Luxembourg on Monday, foreign ministers from the European Union condemned the Gaza blockade as "unacceptable and counterproductive," and called for immediate and unconditional opening of crossings for humanitarian aid.
"The most important part of what we can do is to try and provide support to actually get the crossings open and to ... help people rebuild their homes, to provide for businesses, to try to support everyday things," Catherine Ashton, the EU foreign affairs chief, said.
Tony Blair, the EU's Middle East envoy, expressed hope that an agreement with Israel could be reached within days to allow more material goods into Gaza.
"I hope we are now in a position to move forward in this way. First of all ... whilst Israel will maintain the blockade on weapons and combat material coming into Gaza, that we will change the situation so that those goods that are necessary for ordinary civilian life are brought into Gaza," Blair said.
"In other words, we change from the so-called permitted list of items, where things only come in if they are on that list, to the prohibited list - where things come in unless they are on that list."
Blair also called for the release of Israeli soldier, Gilad Shalit, captured nearly four years ago in Gaza during a cross-border raid.
"He should be released and he should be released unconditionally. That would also help."
Among the proposals being floated are giving the EU a renewed role in managing Gaza's main passenger crossing with Egypt.
B'Tselem, an Israeli human rights organisation, released its own report on Monday documenting dire conditions in the Palestinian territories. The group noted that 95 per cent of Gaza's factories have closed, that 98 per cent of residents suffer from blackouts, and that 93 per cent of Gaza's water is polluted.
Amr Moussa, the secretary-general of the Arab League, on Sunday called for an end to the blockade.
The ICRC also criticised Hamas, the Islamic movement which controls Gaza, for preventing the ICRC from visiting Gilad Shalit, the Israeli soldier captured in 2006. Shalit is entitled to visits from the Red Cross under international law.
"In violation of international humanitarian law, [Hamas] has also refused to allow him to get in touch with his family," the ICRC said.
But the bulk of the ICRC's criticism was directed at Israel's blockade. In addition to the health care problems, the ICRC noted that 40 per cent of Gaza's residents are not connected to a sewage system, and that restrictions on movement have driven many farmers and fishermen into poverty.
One-third of Gaza's farmland is located in a "buffer zone" controlled by the Israeli army, and boats are only allowed to fish within three nautical miles of Gaza's coast.
The ICRC demanded that both Israel and the Hamas government "allow and facilitate rapid and unimpeded passage" of aid shipments to Gaza. Hamas has refused to accept 10,000 tonnes of humanitarian aid seized from the flotilla of aid ships attacked last month by the Israeli army.
The Israeli government announced on Sunday that a panel, chaired by former supreme court judge Yaakov Turkel, would investigate the flotilla attack.