"The persons who have worked on this report, and those who unfortunately have been victims of this terrible and illegal act, are outstanding scientists, and have contributed enormously over the 20, 21 years of the existence of the IPCC," Pachauri told journalists in Copenhagen.

"I believe they are being unfairly targeted," he added.

In his opening statement at the UN Copenhagen conference on Monday, the head of IPCC called the incident as an "illegal act" done by those who continued to deny the existence of climate change.

At a news conference yesterday, Pachauri restated this position stating that the act had been timed to interfere with Copenhagen conference and called for an investigation as well.

"I think this is an illegal act. The only issue that has to be dealt with as far as this occurrence is concerned is to find out who is behind it," he said.

Defending the integrity and veracity of the IPCC and its report in the strongest terms, Pachauri noted that "barring a few isolated voices, people over here are totally convinced of the solidity of the findings in the IPCC report."

Hackers had gained access to the documents of the climate research centre of UK-based East Anglia University and leaked confidential data, including thousands of emails and documents between UK and US scientists over the past 10 years which have led to accusations that scientists exaggerated the crisis.

Some of the excerpts of the e-mails posted read, "I've just completed Mike's Nature trick of adding in the real temps to each series for the last 20 years (i.e. from 1981 onwards) and from 1961 for Keith's to hide the decline."

Another e-mail reads: "The fact is that we can't account for the lack of warming at the moment and it is a travesty that we can't."

Saudi Arabia's negotiator Mohammed al-Sabban had stated that climate science had been "shaken" by the leaked e-mails.

Reacting to this statement, Pachauri said "Wouldn't you expect that? Oil and politics mix very well. I'm not too sure that oil and science mixes very well."

The UN Climate Change Chief noted that incident was not a source of friction at the talks. "I think the science produced by the IPCC is rock-solid."

Earlier, the US Deputy Special Envoy for Climate Change, Jonathan Pershing, criticised the media for blowing the controversy out of proportion and maligning scientists involved in this episode.

"What I think is unfortunate and in fact, shameful, is the way in which some scientists who have devoted their lives are being pilloried in the press without due regard to the process," Pershing said.

"The science is incredibly robust and in fact as we look forward I worry much more about not acting urgently than will ultimately be a small blip on the history of this process," he added.