There is "overwhelming evidence" that the Saudi-led group committed "grave violations against children in Yemen," activists said on Wednesday.

In a letter signed by 20 rights groups, including Human Rights Watch, Amnesty International, and Child Rights International Network, the activists also accused UN chief Ban Ki-Moon of tainting his legacy and caving in to Saudi Arabia.

Last week, the UN published a report on children in Yemen conflict, blaming the Arab coalition for killing 510 and wounding 667 of them during last year. The document also said the coalition was responsible for half the attacks on schools and hospitals in Yemen.

Saudi Arabia responded with outrage, with its UN ambassador Abdallah Al-Mouallimi saying the numbers were "wildly exaggerated." The diplomat added he was "deeply disappointed" and "disturbed" by the UN decision to include the coalition in the document.

'Removal is final'

The oil-rich kingdom pushed for the removal from the blacklist, reportedly threatening to cut off funding to UN's Palestinian relief agency. In addition, Riyadh reportedly enlisted allies from the Organization for Islamic Cooperation and the Arab League to pressure Ban into making the changes.

Al-Mouallimi also warned that the listing would be "counterproductive" to Yemen peace talks. A diplomatic source described the Saudi push as "real blackmail" to the Reuters news agency.

On Monday, the UN said it would temporarily remove the coalition from the blacklist pending a joint review of the cases cited in the report.

Saudi representative Al-Mouallimi, however, said the removal was "irreversible"

"We were wrongly placed on the list," he told reporters. "We know that this removal is final."

Waiting for review

Rights groups decried the changes in the Wednesday letter.

"If the Saudi-led Coalition wants to be removed from the list, it should stop killing and maiming children and bombing schools and hospitals in Yemen - the violations for which it was listed," the groups wrote.

"Allowing governments that commit abuses against children to bully their way off the list makes a mockery of the UN's children protection efforts," said Jo Becker, a director at Human Rights Watch.

Earlier, Ban Ki-Moon's spokesman Stephane Dujarric said the UN was "not walking back" from their report, and that final decision was to be made after the joint review.

"The facts in the report are what the secretary-general believes is credible, verified information gathered from a number of sources, often collected in very difficult circumstances," Dujarric said on Tuesday.

"We will see what the review is, and then we will adjust the list as needed," he added.