Human rights groups fear that the number of people executed in Iran could double this year after reports of a spike in secret hangings at a large prison in the city of Mashad. Iran already executes more people per capita than any country in the world.
Credible information from former inmates indicates that "numerous" undeclared executions have taken place in Vakilabad Prison over the past year, the International Campaign for Human Rights in Iran (ICHRI) said in a statement. Many reportedly were hanged in groups.
Most learn their time on death row is up just hours before they are sent to the gallows and their families are given no warning, former prisoners have said. The bodies are returned the following day, once relatives have paid the cost of the rope used in the hanging, one ex-prisoner told the ICHRI, a New York and Netherlands-based non-governmental organisation.
Ten Vakilabad prisoners are said to have been executed together on October 12. More than 600 inmates remain on death row, most of them apparently for drugs offences, the ICHRI said. Mashad lies on a major narcotics smuggling artery from Afghanistan, Europe's main supplier of heroin.
Ahmad Ghabel, a religious scholar critical of the government, documented at least 50 executions during the three months he spent at the prison earlier this year. Another former inmate told the ICHRI that he saw 46 prisoners hanged on a single day in October 2009.
"These reports…indicate that Iran is executing even more people - dramatically more - than now estimated, and possibly twice as many as last year," Aaron Rhodes, an ICHRI spokesman said in a telephone interview from Hamburg, Germany. "We are concerned that if these executions are, in fact, taking place in Mashad, then are other prisons executing in secret also?"
Iran does not allow human-rights rapporteurs into the country. Amnesty International has been investigating similar reports from former inmates and families of prisoners at Vakilabad but has yet to complete its findings. However, Drewery Dyke, its London-based Iran expert, said in an interview: "We regard these allegations as credible".
Analysts say the rising use of capital punishment probably reflects the ascendancy of hardliners in Iran's judiciary, which has also been meting out extreme forms of corporal punishment in recent months.
Iran's deputy judiciary chief, Ebrahim Raisi, this week hailed the recent amputation of a thief's hand as a "divine punishment" and "source of pride".
The authorities do not release the numbers of those hanged or their names, and have not acknowledged any secret, mass executions.
Mr Ghabel, the religious scholar, told the ICHRI that executions at Vakilabad were not publicised to "avoid a huge international uproar". He was freed on bail in June but detained again last month after speaking publicly about the group executions at Vakilabad. His wife says he suffers from heart disease.
While the Iranian authorities are sensitive to international criticism of their human-rights record, officials at Vakilabad do not mind word of group executions leaking out locally because they are meant to intimidate drug smugglers, observers say.
"It appears the judiciary chief, Sadegh Larijani, unlike his precedessor, doesn't believe in keeping down the number of executions, particularly for drug-related crimes," said a senior analyst in Tehran, who spoke on condition of anonymity because of the sensitivity of the subject.
At least 388 were executed last year, compared to 85 in 2005, the year that President Mahmoud Ahmadinejad took office.
Only China executes more of its citizens.
Vakilabad's inmates know when executions are imminent, but not whose turn it will be.
Phone lines at the facility are cut off at 4pm so that the news cannot be relayed beyond its walls, former inmates told ICHRI.
All prisoners are returned from the yard to their cells. Only then are the names of the condemned announced over a loudspeaker. Those about to die are removed from their cell blocks for ritual religious cleansing and to write their wills.
"Families, lawyers and prisoners themselves… have no idea when the executions will be carried out, let alone [having the family] present during the executions," a former inmate said.
Under Iranian law, families must be informed of an execution so that they can visit the prisoner and even attend the hanging.
Capital offences in Iran include murder, rape, drug trafficking, armed robbery, adultery, treason and espionage. The authorities insist that the death penalty is essential for maintaining public security and that is applied only after exhaustive judicial proceedings.
But human-rights groups say that many accused of drug offences and other serious crimes are often held for long periods in pre-trial detention, routinely ill-treated and allowed only limited access to a lawyer.
The ICHRI said in a statement: "According to multiple accounts, the majority of inmates on death row were convicted for narcotics-related crimes. Some reported that they were tortured and forced to make confessions, but that trial judges ignored their claims of physical coercion."
Much of Iran's crime is drug-related. In the past two decades, Iran has lost more than 3,500 law enforcement officers in clashes with heavily armed smugglers on its border with Afghanistan.
By blocking Afghan heroin from reaching Europe, Iran also suffers a costly spillover effect: it is flooded with cheap heroin and opium and is believed to have the world's highest addiction to both.
But high youth unemployment and social problems also contribute to high drug addiction and crime rates, analysts say.
Mr Rhodes of the ICHRI said: "The authorities are trying to curb these problems by using extreme punishments, which violate Iranian and international law, in an increasingly brutal policy of intimidation."