Relatives of rebels, activists and ordinary people who have gone missing in a Pakistani province have appealed to the UN for help after walking across Pakistan for months to draw attention to their plight.

Dozens of those who say their family members were abducted or killed reached Islamabad on Thursday after a 2,300km walk from Balochistan which started last October - a rare act of dissent by the often frightened relatives of the abductees.

The group of about 50 people said they would submit a petition to the UN asking for help and to draw attention to their problem.

Bodies of hundreds of pro-independence rebels have been found across the Balochistan province and many more have gone missing in the past several years, in a little-reported conflict in a remote corner on Pakistan's Iranian border.

Baluch activists say the bodies are evidence that the army is pursuing a systematic "kill and dump" campaign to crush pro-independence dissent - a charge the army has repeatedly denied.

"Finally we have decided to go to the UN and make our voice heard about the atrocities against the Baluch people who are being picked up and whose bodies are being dumped on a daily basis," Mama Qadeer Baluch, the group's 72-year-old leader, said.

The group has made appeals to the UN and other international organisations in the past, but with little success.

Delegations have in recent years visited Balochistan on fact-finding missions to investigate the claims.

'Threats and abuses'

Speaking under a stormy Islamabad sky, Baluch told Reuters news agency his group faced pressure and often abuse from some people they encountered in towns and villages across Pakistan, a testament to broader tensions between the Baluch and other ethnic groups.

"In Punjab, threats and abuses were hurled into our faces," said Baluch, wearing a traditional turban and white robes.

Neither the government nor the army were immediately available for comment on Thursday.

But they have always denied allegations of widespread human-rights violations in Balochistan, branding separatists as terrorists and alleging they are backed by India.

Baluch, founder of the advocacy group Voice for Baloch Missing Persons, said they set off from Quetta on October 27, 2013, and have been on foot ever since.

Groups of young men wearing air pollution masks to conceal their identities have joined the group from nearby cities to protect it from possible abuse or violence, as the procession reached the outskirts of Islamabad on Thursday.

Recalling an incident in an area called Sarai Alamgir in the district of Gujrat, Baluch said his group was intercepted by a car carrying four men who shouted abuse at them.

"We don't have any hope for the government of Pakistan and its Supreme Court. We have been protesting for the last five years, we have set up protest camps in Karachi, Quetta and visited Islamabad several times," Baluch said.

"But ... the government ... is not listening to us," he said. "When we are not being heard by the government, it is natural that we should knock on the other door."