"I do not believe Kofi Annan ever agreed with the position of the United States on its handling of the Iraqi crisis and in particular on its assertion that Iraq was in possession of weapons of mass destruction," the former adviser said.
Kofi Annan, the source added, never supported the pretexts and misinformation provided to justify the invasion and destruction of Iraq.
It took a huge amount of courage and leadership for the then-UN Secretary General to go against the interests of the most powerful country at the United Nations, the ex-adviser said.
The source also pointed out that Kofi Annan did everything in his power to prevent the bombing of Iraq and called the war illegal.
Sunday marks 20 years since then-Secretary of State Colin Powell delivered his infamous speech at the UN Security Council outlining the Bush administration's case that Baghdad possessed weapons of mass destruction, which provided the crucial pretext for the US invasion of Iraq.
In March of 2003, the US and a group of allies dubbed the "coalition of the willing," invaded Iraq, six weeks after Powell's speech.
The following fall, a CIA report submitted to Congress concluded that there were no WMDs in Iraq when the US launched the invasion. Powell would later describe the speech as a "blot" on his record and great intelligence failure.
Despite the fact WMDs were never found, the war in Iraq raged on until 2011.