UPDATE 1-Guatemala president must not impede anti-corruption body - UN

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GENEVA, Aug 29 (Reuters) - The United Nations on Tuesday said it was "disturbed" by the decision of Guatemala's president to expel the head of a U.N.-backed anti-corruption unit investigating his campaign financing.

It called for guarantees judicial figures would be protected.

Guatemalan President Jimmy Morales on Sunday ordered the expulsion of Ivan Velasquez, a veteran Colombian prosecutor who leads Guatemala's International Commission against Impunity, known as CICIG.

Morales said the expulsion was a matter of foreign policy and therefore the responsibility of the executive, not the courts. But his order was suspended by the nation's top court hours later.

"I am deeply disturbed by the unprecedented decision of the president of Guatemala," U.N. human rights chief Zeid Ra'ad al-Hussein said in a statement.

"I call on the Guatemalan government to allow CICIG to carry out its work unimpeded and to take steps to guarantee the protection of human rights defenders, judicial officials, including the attorney general and high court judges, as well as CICIGs staff."

Velasquez and CICIG, together with the office of Attorney General Thelma Aldana, play a critically improtant role in the fight against corruption and impunity, Zeid said.

The Geneva-based International Commission of Jurists said failure to comply with the Constitutional Court ruling could constitute "obstruction of justice," a criminal offense.

"The president`s decision to declare Ivan Velasquez as 'non grata' and ordering his immediate removal from the country is in clear breach of international law," the ICJ said in a statement.

CICIG wants Morales, a former comedian elected on an anti-corruption ticket last year, to be investigated over alleged illicit funding during his election campaign.

He has denied any wrongdoing but CICIG is investigating some $800,000 in allegedly unexplained contributions to his campaign.

Following Morales' announcement on Sunday, hundreds of Guatemalans took to the streets, mostly to defend Velasquez outside his offices and in the center of Guatemala City.

Some groups came out in support of the president and against foreign interference.

Many politicians in Guatemala consider the foreign-led body, which is unusual among U.N. bodies for its powers to bring cases to prosecutors, to be a violation of national sovereignty. Anti-corruption activists credit it with cleaning up government.

It is responsible for the arrests of at least 15 current and former members of Congress on corruption charges. (Reporting by Tom Miles, editing by Stephanie Nebehay)