(Updates with response by Eritrea)
March 22 (Reuters) - The European Union on Monday imposed sanctions on Eritrea over human rights violations and blacklisted the country's National Security Office, which is tasked with intelligence gathering, arrests and interrogations.
At the beginning of March, the United Nations said Eritrean troops were operating throughout Ethiopia's northern Tigray region and reports suggested they were responsible for atrocities.
Tigray has been gripped by conflict since November last year when Ethiopia's federal forces moved in and toppled the region's then ruling party, the Tigray People's Liberation Front (TPLF).
In a statement, Eritrea rejected the accusations, saying they were trumped up and the sanctions had no legal basis.
"The National Security Office is responsible for serious human rights violations in Eritrea, in particular arbitrary arrests, extrajudicial killings, enforced disappearances of persons and torture," the EU said after foreign ministers of the 27-nation bloc agreed the measures.
The sanctions mean an asset freeze in the EU. Additionally, individuals and entities in the EU are prohibited from making funds available, either directly or indirectly, to those listed.
Eritrea accused the EU of aiming to bring the TPLF back to power and said the sanctions were a "futile attempt to drive a wedge between Eritrea and Ethiopia."
"The EU has no legal or moral prerogative for its decision and has merely invoked trumped-up charges to harass Eritrea for other ulterior motives," Eritrea's Foreign Affairs Ministry said.
Ethiopia and Eritrea have denied the involvement of Eritrean troops in the fighting alongside Ethiopian forces, although dozens of witnesses, diplomats and an Ethiopian general have reported their presence.
Thousands of people have died amid the fighting, hundreds of thousands have been forced from their homes and there are shortages of food, water and medicine in Tigray, a region of more than 5 million people.
The EU is considering imposing further sanctions on Eritrea. (Reporting by Sabine Siebold; Editing by Bernadette Baum, William Maclean)