Hundreds of political activists are being held and tortured by security forces in the Pakistani province of Balochistan, Human Rights Watch says.
The region is currently the centre of an insurgency by local tribesmen fighting for greater political rights.
A new report by the rights group focuses on political activists detained without charge. Many of them were later killed, the report says.
The Supreme Court is investigating the killings and disappearances.
Entitled "We can torture, kill and keep you for years", the report completes a three-part series of investigations on Balochistan by Human Rights Watch (HRW).
The BBC's Syed Shoaib Hasan says that taken together they present a disturbing and violent picture of what many are calling Pakistan's secret dirty war.
"Pakistan's security forces are engaging in an abusive free-for-all in Balochistan as Baloch nationalists and suspected militants 'disappear' and in many cases are executed," HRW Asia Director Brad Adams said.
"The national government has done little to end the carnage in Balochistan, calling into question its willingness or ability to control the military and intelligence agencies."
Pakistani authorities routinely deny claims of abuses in Balochistan.
The latest 132-page report says state security remains responsible for most of the abuses.
This includes holding detainees as young as 12 years old without charge - as well as the increasing torture and killing of those held, it says.
File photo of paramilitary soldiers on guard near the site of a shooting on the outskirts of Quetta June 22, 2011. Balochistan is the scene of frequent attacks
The report details 45 alleged cases of enforced disappearances, the majority in 2009 and 2010. It says that while hundreds of people have been "forcibly disappeared" in Balochistan since 2005, dozens of new enforced disappearances have occurred since Pakistan returned to civilian rule in 2008.
The report is based on over 100 interviews by HRW in Balochistan in 2010 and 2011 with family members of "disappeared" people, former detainees, local human rights activists, lawyers and witnesses to government abductions.
It says that those targeted are primarily Baloch nationalist activists or suspected Baloch militants.
"Pakistani security services are brazenly disappearing, torturing, and often killing people because of suspected ties to the Baloch nationalist movement," Mr Adams said. "This is not counterinsurgency - it is barbarism and it needs to end now."
Security officials in Balochistan routinely dismiss such claims as part of propaganda by separatists.
They say all those arrested have been produced in courts.
In a recent interview, the top security official in Balochistan told the BBC the killings were the result of infighting amongst the nationalists.
But other security officials have also told the BBC that they have detained the activists.
They say the insurgents are being supported by India and it is the duty of Pakistan's security forces to do their utmost to suppress them.
The report also highlights how difficult conditions are getting for ordinary citizens in Balochistan. The province has strategic importance as it borders Iran and Afghanistan.
US officials say the Afghan Taliban leadership have their headquarters in the province, a claim Pakistan denies.
Balochistan, Pakistan's largest and most sparsely populated province, is also rich in minerals - with vast untapped deposits of oil, gas, copper and gold.
But locals say most of this remains under the control of the federal government - its policies have left them little choice, many say, but to side with the insurgents.