UNITED NATIONS — The United States and Israel on Thursday slammed a call by an outspoken UN rights expert for a boycott of companies helping Israel's settlement expansion in the Palestinian territories.

US Ambassador to the United Nations Susan Rice said the boycott appeal by Richard Falk would "poison the environment for peace." An Israeli spokeswoman criticized the "distasteful sideshow."

Falk, the UN special rapporteur on human rights in the occupied Palestinian territories, said the UN General Assembly and civil society should boycott international firms that help expand Israeli settlements.

He singled out Caterpillar, Hewlett Packard and Motorola of the United States, Veolia Environment of France, G4S of Britain, Dexia of Belgium, Volvo Group and Assa Abloy of Sweden, Ahava, Elbit Systems and Mehadrin of Israel, Riwal Holding Group of the Netherlands and Cemex of Mexico.

He said all were involved in building and maintaining Israeli settlements in the occupied territories that the United Nations, United States and European Union all consider illegal.

Israeli-Palestinian talks have been frozen for more than two years over the settlement expansion and Falk added his voice to warnings by Palestinian and international leaders that the construction threatens hopes for separate Palestinian and Israeli states.

"All Israeli settlements in the West Bank, including East Jerusalem, have been established in clear violation of international law," said Falk, who highlighted that the settlements now make up more than 40 percent of the West Bank.

Speaking before the General Assembly, he called for boycotting businesses tied to settlement expansion "until they bring their operations into line with international human rights and humanitarian law and standards."

The United States quickly hit out at the statement by Falk, a Princeton University international law professor who has labeled Israel's 2008 offensive against Gaza as "war crimes" and courted controversy with comments on the origins of the September 11, 2001 attacks on the United States.

"His call for a boycott of private companies is irresponsible and unacceptable," said Rice, the US envoy to the UN.

"Throughout his tenure as special rapporteur, Mr Falk has been highly biased and made offensive statements, including outrageous comments on the 9/11 attacks."

Falk's "recommendations do nothing to further a peaceful settlement to the Israeli-Palestinian conflict and indeed poison the environment for peace," the US ambassador added, saying his work as a UN special rapporteur "only damages the credibility of the UN."

Karean Peretz, spokeswoman for the Israeli mission to the United Nations dismissed Falk's "grossly biased report, based on a one-sided mandate, which is completely divorced from reality."

"Falk's distortions of both fact and law are countless. While he spends pages and pages attacking Israel, Falk fails to mention even once the horrific human rights violations and ongoing terrorist attacks by Hamas" in Gaza, the spokeswoman added.

Falk is named by the UN Human Rights Council, not by UN leader Ban Ki-moon.