Human rights abuses in Eritrea force about 3,000 people to flee every month despite a "shoot-to-kill policy" targeting those trying to leave, the United Nations has said.

Special human rights rapporteur Sheila Keetharuth said the UN refugee agency was concerned about 305,723 Eritreans who have fled over the past decade.

"The most serious human rights violations are being committed" in Eritrea, she said, including extrajudicial killings, disappearances, extended incommunicado detention, torture, indefinite national service and lack of freedom of expression, assembly, religious belief and movement.

She told the general assembly's human rights committee on Thursday that "excessive militarisation" in the country and indefinite national service for all Eritreans aged 18 to 50, often without adequate remuneration, "causes countless Eritreans to desert their positions and flee the country."

Eritrea's UN ambassador Arya Desta rejected Ms Keetharuth's report, claiming that human rights issues are being used "as a tool of political pressure."

He accused unnamed countries of spearheading the imposition of "unfair and unjust" sanctions.

Eritrea has barred Ms Keetharuth from the country but she said she had spoken to Eritrean refugees in Ethiopia, Djibouti and elsewhere.

Ms Keetharuth called for democratic national elections, an immediate accounting of those held incommunicado including journalists who have been imprisoned since 2001, demobilisation of all those who have completed 18 months of national service and an immediate halt to the "shoot-to-kill" policy.