A top UN rights expert called Friday for Israeli settlements to be classified as war crimes, urging the international community to finally demand accountability for a practice it has long deemed illegal.

Presenting his latest report to the UN Human Rights Council in Geneva, Michael Lynk, the United Nations special rapporteur on the rights situation in the occupied Palestinian territories, said the settlements constitute a "violation of the absolute prohibition against settler implantation".

This practice, which involves an occupying power transferring parts of its civilian population into an occupied territory, was designated as a war crime in the 1998 Rome Statute of the International Criminal Court.

Lynk insisted that "this finding compels the international community to assess the plentiful accountability measures on its diplomatic and legal menu."

It was time, he said, "to make it clear to Israel that its illegal occupation, and its defiance of international law and international opinion, can and will no longer be cost-free."

Israel, which does not recognise Lynk's mandate and has never granted him access to the Palestinian territories, boycotted the session.

The expert pointed to the wide range of UN resolutions labelling Israel's settlement activity as illegal.

"The illegality of the Israeli settlements is one of the most settled and uncontentious issues in modern international law," he said.

But, Lynk added, "it is a tragic paradox that, while the Israeli settlements are clearly prohibited by international law, the international community has been remarkably reluctant to enforce its own laws."

The UN expert said the number of Jewish settlements had reached almost 300 in occupied East Jerusalem and the West Bank, with more than 680,000 Israeli settlers.

The settlements have become "the engine of Israel's 54-year-old occupation, the longest in the modern world”, Lynk added. 

International action, not just words, was needed to resolve the situation, he said.

"As long as the international community criticises Israel without seeking consequences and accountability, it is magical thinking to believe that the 54-year-old occupation will end and the Palestinians will finally realise their right to self-determination."