GENEVA (Reuters) - Eritrea now has "effective control" of parts of Ethiopia's Tigray region, a U.N. human rights expert said on Tuesday, calling for troops to withdraw and for a prompt investigation into abuses, including the abduction of refugees.

       Mohamed Abdelsalam Babiker, U.N. special rapporteur on human rights in Eritrea, was addressing the Human Rights Council a day after he presented a report that described violations by Eritrean troops in Tigray, including summary executions and the abduction and disappearance of Eritrean refugees there.

       Eritrea sent troops to Tigray after the Ethiopian military launched an offensive in November in response to attacks on federal government bases by regional forces. Eritrea denied for months that its troops were in Tigray, but later acknowledged their presence while denying they were responsible for abuses.

       "According to information that I have, Eritrea has an effective control over the Tigray region...especially in the two camps: Hitsats and Shimelba," Babiker said, referring to camps in Tigray that house refugees from Eritrea.

       The United Nations has said Eritrean refugees were attacked and abducted from the camps by armed men suspected to be Eritrean troops.

       "The whereabouts of refugees who remain missing is really a matter of great concern," Babiker said, calling for a full investigation by an independent body into these allegations.

       Eritrea's foreign affairs ministry responded on Tuesday to the report with a lengthy statement in which it said that the Geneva-based council had targeted Eritrea for more than a decade through politically-motivated and flawed reporting.

       The ministry said allegations of sexual violence and other war crimes by Eritrean forces in Tigray were baseless. In comments on Monday, the Eritrean delegate told the forum that the Special Rapporteur's role should be abolished.

       During the debate, other countries including the United States criticised the presence of Eritrean troops and referred to "credible reports" that Eritrea was forcibly returning Eritrean refugees to their homeland.

       Fighting since November between Ethiopia's government and the region's ousted ruling party, the Tigray People's Liberation Front (TPLF), has displaced more than 2 million people.

       Eritrea agreed to withdraw its troops from Ethiopian territory along their mutual border, Ethiopia's Prime Minister Abiy Ahmed said in March.

       (Reporting by Emma Farge; Editing by Stephanie Nebehay and Peter Graff)