At least six Red Cross workers have been killed by suspected Islamic State gunmen in northern Afghanistan, officials say.

Two others are missing after the attack in the volatile northern province of Jowzjan, the group has said.

The workers were carrying supplies to areas in the north of the country hit by deadly snow storms and avalanches.

"We can confirm that six of our colleagues were killed and two are unaccounted for in Jowjzan province," a spokesman for the International Committee of the Red Cross (ICRC) said.

"We are shocked and devastated."

The organisation's statement added: "It is not yet clear who carried out the attack or why."

However, Jowzjan provincial governor Lotfullah Azizi, using the Arabic name for Islamic State, said: "Daesh is very active in that area."

Jowzjan police chief Rahmatullah Turkistani said the Red Cross workers' bodies are now in the provincial capital and an operation had been launched to find the two missing group members.

None of the identities and nationalities have yet been released.

A spokesman for the Taliban said his group was not involved in the attack and promised Taliban members would help find those responsible.

IS has made limited inroads in Afghanistan but has carried out increasingly deadly attacks.

The latest killings underscore the dangers faced by aid workers in the country.

In December, a Spanish employee of the ICRC was abducted when workers from the charity were travelling between the northern city of Mazar-e-Sharif and the neighbouring volatile Taliban hotbed of Kunduz.

He was released nearly a month later, but other charities have suffered similar tragedies.

In April 2015, five Afghan workers for Save the Children were found shot dead after they were abducted in the southern province of Uruzgan.

The ICRC said recently increasing insecurity was making it difficult to provide aid to many parts of the country.