A UN report seen by Reuters says the Taliban and its allies are believed to have killed scores of former Afghan officials, security force members and people who worked with the international military contingent since the US-led pullout.

UN Secretary General Antonio Guterres’ report to the UN Security Council paints a picture of worsening living conditions for Afghanistan’s 39 million people despite an end of combat with the Taliban's takeover in August.

"An entire complex social and economic system is shutting down," Guterres said.

The report sounds the latest in a series of warnings the UN chief has issued in recent months about the humanitarian and economic crises that accelerated after the Taliban seized Kabul as the last US-led foreign troops left and international donors cut critical financial aid.

Guterres recommended the council approve a restructuring of the UN mission to deal with the situation, including the creation of a new human rights monitoring unit.

The UN mission "continues to receive credible allegations of killings, enforced disappearances and other violations" against former officials, security force members and people who worked for the US-led international military contingent despite a general amnesty announced by the Taliban, the report said.

The mission has determined as credible reports that more than 100 of those individuals have been killed – more than two-thirds of them allegedly by the Taliban or their affiliates – since August 15, it said.

There also are credible allegations of the extra-judicial killings of at least 50 people suspected of belonging to the local branch of the Islamic State militant group, according to the report.

"Human rights defenders and media workers continue to come under attack, intimidation, harassment, arbitrary arrest, ill-treatment and killings," it said.