Professor Yves Cabannes, a UN adviser on forced eviction, this week visited Dale Farm near Basildon, in Essex, where a mass clearance is due to begin on Monday.
He said: "A study which I led on forced eviction found that at Dale Farm and the UK in general, the Government is violating international human rights law on three points.
"These are the right to adequate housing, the right to be defended from forced eviction and discrimination."
But the UN's human settlements programme, UN-Habitat, later issued a statement saying: "The press conference held at Dale Farm is an initiative of individuals of the Advisory Group on Forced Evictions. UN-Habitat is not involved in that event."
During the press conference, Professor Cabannes added that Basildon Council had failed to provide the pitches it should make available to travellers.
He said: "The people who are abusing the law are the council not the travellers. The council is not fulfilling its duties. There are many Dale Farms which face these issues every day and there needs to be a co-ordinated approach across the country.
His visit came as there were signs of travellers beginning to leave the site voluntarily. At least five caravans are believed to have left on Tuesday night and a large chalet was seen being removed on two trucks on Wednesday afternoon.
Leader of Basildon Council Tony Ball dismissed Mr Cabannes's comments. He said: "For 10 years, we have sought a peaceful and humanitarian solution to Dale Farm, but it must be one that involves upholding the law of our country. The current site has been illegally developed. After 10 years when we have exhausted the judicial process and every effort to negotiate we have no option but to resort to direct action to clear the site."