It was the first time that the destruction of the statues had been independently confirmed, despite a concerted effort by Arab, Islamic and international players to spare them.
"I was distressed to learn from my special envoy, Pierre Lafrance, that the destruction of the Bamiyan Buddhas has been confirmed," the UN cultural body's chief Koichiro Matsura said in a statement.
"It is abominable to witness the cold and calculated destruction of cultural properties which were the heritage of the Afghan people, and, indeed, of the whole of humanity," the statement said.
The Taliban had said the huge figures, carved into sandstone cliffs in Bamiyan city more than 1,500 years ago when Afghanistan was a seat of Buddhism, are "false idols" and must be destroyed in line with Islamic laws.
Prime Minister Atal Behari Vajpayee of India, which has a large Buddhist population, on Monday branded the destruction "an act of barbarism" but stressed that his government had been helpless to intervene.
"What is happening there has been condemned by the entire world. It is an act of barbarism, but there is a limit and the world cannot stop the destruction," said Vajpayee.
Yet there were no shortage of efforts to try reversing the Taliban's edict, including from many Muslim countries and Pakistan, the closest ally of the Taliban and one of only three countries which recognizes its puritanical regime.
After talks over the weekend between Pakistan Interior Minister Moinuddin Haider and Taliban officials failed, Haider played for time "suggesting that since this edict has repercussions for the entire Muslim world, it should be discussed with the ulema (Islamic religious leaders) from outside Afghanistan."
The Taliban said the clerics had "failed to convince us that destroying the statues was un-Islamic."
They were part of a delegation of the Organisation of the Islamic Conference (OIC) led by Qatar's foreign minister and included Egypt's top religious leader and two leading Sunni clerics, the same faith as the Taliban.
"From a religious point of view it is clear, these statues are part of humanity's heritage and do no affect Islam at all," said the Egyptian cleric, speaking on his return to Cairo.
A similar diplomatic mission from Japan also failed to overturn Taliban Supreme Leader Mullah Mohammad Omar's decree, which he said was based on orders of God and the Koran, Islam's holy book, and was "irreversible."
UN Secretary General Kofi Annan tried his hand at convincing the Taliban not to carry out their "lamentable decision," meeting Taliban Foreign Minister Wakil Ahmad Mutawakel while on a tour of South Asia.
Annan stressed that many Islamic countries opposed the move, adding that destroying cultural masterpieces was not the way to mobilise the donor community to help Afghanistan overcome its humanitarian crisis.
Jordan, another Muslim country, was quick to react to the news Monday that the statues were finished, saying it was disappointed at the "failure of Arab, Islamic and international efforts to stop the destruction."
"Heritage that dates back to before Islam belongs to the entire world," the country's culture minister said.
With the Taliban set to move even further into isolation now, Matsuria concluded that "the loss is irreversible" but that "everything possible must be done to stop further destruction" of Afghanistan's pre-Islamic heritage.
He also said he hoped that the destruction "will not provide fanatics elsewhere with an excuse for acts of destruction targeting Muslim cultural properties."