"Things are not moving forward. On the contrary we must admit that the international community has largely failed in ensuring access to the necessary humanitarian aid," Bonino said during a meeting with the UN Under-Secretary General for humanitarian affairs Valerie Amos.
Bonino said "practically everything is ready to be taken into Syria to alleviate suffering," but diplomacy and negotiations had failed to ensure access.
"The question is not whether we have enough medicine, food, transport, means of distribution. All this is ready, so the shame falls on us," she added.
Her comments came after 10 days of inconclusive Geneva peace talks between the Syrian government and opposition delegations, which failed to reach an accord on granting greater humanitarian access, particularly in besieged areas like the Old City of Homs.
Western nations are now planning a UN Security Council resolution on the issue, which could be ready this week.
The immediate focus is on the fate of an estimated three million people trapped in areas where there is fighting, or blockaded by government or rebel guns.
"Extensive human rights abuses and violations of international humanitarian laws are making the Syrian crisis the worst humanitarian tragedy of our times in terms of number of civilians involved," Bonino said.
Despite not being on the agenda at the Geneva talks, aid has entered the besieged Palestinian refugee camp Yarmuk on the outskirts of Damascus.
However, UN trucks carrying enough food for more than 2,500 people trapped in the Old City of Homs have been prevented access by the Syrian government, which voiced fears the aid would fall into the hands of "armed and terrorist groups" in the city.
The city of Homs has been under siege since June 2012 after rebels there rose up against the regime.
There has been no progress so far on an evacuation, which the opposition fears could be tantamount to expelling the population of rebel-held areas.
The opposition says convoys must be allowed to deliver supplies to civilians who want to stay in their embattled community.