An "alarming" rise in Iran's execution rate since the beginning of the year has drawn sharp criticism from Iranian opposition leaders, western nations and rights groups.
Amnesty International recorded more than 80 executions last month, nearly as many as were put to death in all of 2005, when President Mahmoud Ahmadinejad took office.
Human Rights Watch (HRW) warned that Iran is heading towards hanging a record number of more than 1,000 people before the end of the year.
Iran's two main opposition leaders, Mir Hossein Mousavi and Mehdi Karrubi, urged "that these unrestrained and illogical executions be halted".
The hangings have only managed to "spread fear" among the people and "forced further isolation of Iran in the international community", they said in a statement on Wednesday.
The two men slammed the judicial authorities for allegedly executing prisoners without due process or the knowledge of their families and lawyers.
The United States, the European Union and the UN's human rights commissioner have also expressed dismay and urged the Iranian government to halt executions.
Iran, the world's most prolific executioner, in turn has angrily told western nations to mind their own business.
Tehran's foreign ministry spokesman, Ramin Mehmanparast, said last Tuesday: "Why do they make such noise over a person executed for [drugs] smuggling or someone on trial over adultery, while they do not defend thousands of Palestinians who innocently die?"
The vast majority of those executed in Iran are alleged drug traffickers, many caught trying to smuggle heroin from neighbouring Afghanistan, destined for the streets of European cities.
"If Iran does not combat drugs, Europe and the West will be hurt," Mr Mehmanparast said.
But the UN's human rights chief, Navi Pillay, said on Wednesday that at least three hanged in January were political prisoners while more reportedly remain on death row. Mr Pillay said: "Dissent is not a crime."
Rights activists say many accused of capital crimes are often held for long periods in pre-trial detention, routinely ill-treated and allowed only limited access to a lawyer.
A spokesman for the International Campaign for Human Rights in Iran, Aaron Rhodes, said: "It seems that life is becoming cheaper and cheaper in Iran. The situation resembles more and more periods in the 1980s when huge numbers of people were summarily executed.
"Death sentences for drug-related crimes are not considered legitimate by UN authorities because they are not considered to be the most serious crimes."
A growing number, rights activists say, are also being executed on the vague charge of "moharebeh", or enmity against God.
"This has become a kind of catch-all to charge political dissidents," Mr Rhodes said.
"According to the Iranian criminal code, it can only apply to those who have been found with weapons and used them in violent attacks against the state. That's clearly not the case with many on death row for this capital offence."
Iran is second only to China, a far more populous country, in the number it executes.
At least 388 people were hanged in 2009, against at least 94 executions for all of 2005. In 2010, Amnesty International recorded about 250 executions that the Iranian authorities acknowledged.
However, the rights group received "credible reports" of hundreds of other executions not officially acknowledged, mostly in Vakilabad Prison in Mashhad.
Analysts in Tehran are sceptical of speculation in some western media that Iran is taking advantage of the world's pre-occupation with events in Egypt to ratchet up executions to strike fear into the opposition Green movement and ward off possible new street protests.
"If there is any such intention, it is secondary to the judiciary's desire to clear out overcrowded prisons of death-row inmates, some of whom were sentenced years ago," said one expert.
"The judiciary chief, Sadegh Larijani, is a real hardliner," he added. "As drugs are a huge problem, people like him also hope to get the people's support by hanging traffickers."
In battling drugs smuggling from neighbouring Afghanistan, Iran 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.
Drewery Dyke of Amnesty International in London said there was a "growing view in some judicial circles in Iran that prisons are overcrowded and need clearing".
"Officials have stated their desire to ensure a swifter implementation of the death penalty" for drugs offences.
Drug offenders are tried in opaque and generally unfair procedures that often do not include a right to appeal, Mr Dyke said.
He believes any political message is secondary, but nevertheless unmistakable: "An underlying message here is that if you step out of line, this is what can happen to you."
The US last week urged Iran to halt executions, saying it was particularly troubled by the hanging on January 29 of a Dutch-Iranian national, Zahra Bahrami, after she was denied consular access.
She was reportedly arrested in December 2009 after joining an anti-government demonstration while visiting relatives, and originally accused of moharebeh. But she was eventually charged and found guilty of drugs offences. The Dutch government suspended diplomatic relations with Iran in response to her execution.
Europe's chief diplomat, Catherine Ashton, expressed "dismay" last week that the Iranian authorities denied Bahrami, 46, access to consular officials before her execution and failed to ensure a "fair and transparent judicial process".
Capital offences in Iran include murder, rape, drug trafficking, armed robbery, adultery, treason and espionage. The authorities insist the death penalty is essential for maintaining public security and that it is applied only after exhaustive judicial proceedings.
Bahrami said she was tortured into confessing and denied the charges, according to her family and rights groups. Her distraught and angry daughter, Banafsheh Nayebpour, quoted by the International Campaign for Human Rights in Iran, said neither the family nor Bahrami's lawyer had been officially informed of the hanging.
Under Iranian law, families must be informed of an execution so that they can visit the prisoner and even attend the hanging.
"Did I not have the right to see her before her execution?" Ms Nayebpour said. "Is it so easy that my mother is no longer in this world?"
