On January 27, Iran executed two men charged with moharebeh, or "enmity with God." Ali Zamani and Arash Rahmanipour were the first Iranians hanged for their alleged connection with demonstrations following Iran's disputed presidential election last June. In fact, though, security forces had arrested both Zamani and Rahmanipour weeks before the election.

Nevertheless, the authorities paraded the two detainees in front of cameras from state-run TV, along with hundreds of other political dissidents who were arbitrarily detained in the post-election crackdown. Like Zamani and Rahmanipour, many of these dissidents had not actually participated in any of the peaceful demonstrations. By executing  Zamani and Rahmanipour-arrested for their alleged ties to an unpopular pro-monarchist group -Tehran is putting the world on notice that government critics will be  treated as members of  foreign-based "terrorist" networks and that they will be punished accordingly.

 Zamani and Rahmanipour's executions were widely seen to have paved the way for more executions of political prisoners in the coming months. And indeed, only a few days after the executions, the Judiciary announced the impending execution of at least nine more people tied to the post-election unrest.

Notwithstanding these developments, Japan has chosen to remain silent. In fact, Japan has had little to say about the outrageous human rights violations that have taken place since mid-June-the killings of peaceful demonstrators in the streets and in prisons, the arbitrary arrest of hundreds of political dissidents, and the torture and sexual assaults in prisons. Instead, Tokyo merely issued two statements expressing "concern" about the violence and calling on the Iranian government to find a "peaceful resolution" to the conflict.

Japan's modus operandi vis-à-vis Iran is perhaps not surprising given Tokyo's longstanding view toward Tehran as a major trading partner, and a "friend."  As of 2006, Japan was Iran's second- largest trading partner, after China. Iran is Japan's largest importer of crude oil after Saudi Arabia and the United Arab Emirates.  In addition, Japan has provided at least another $1 billion in loans, grants and technical cooperation funds to Tehran.   

For its part, Tokyo denies it has kept silent when it comes to diplomacy with Iran, maintaining that it prefers to deal with Tehran via inconspicuous bilateral talks. Yet, with the exception of Japan's instrumental role in the 2009 release of the journalist Roxanne Saberi (the daughter of an Iranian father and a Japanese mother held in Tehran's notorious Evin Prison), Tokyo has had little to show for its closed-door diplomacy when it comes to Iran's dreadful human rights record.

Undoubtedly, it is sometimes appropriate for nations to adopt a multi-pronged diplomatic strategy to deal with governments like Iran's. But there are moments when even the most conservatively inclined and cautious friend needs to speak up.

That moment, for Japan, is now.

As a major trading partner and an influential world power, Japan has a unique role to play when it comes to Iran. It is time for Tokyo to make a clear demand to Tehran to end state-sponsored violence against peaceful protesters and government critics, and to call for the immediate release of all political prisoners. It is time for Tokyo to tell Tehran that it needs to open a transparent and comprehensive investigation into the killings, arrests and detentions of thousands of demonstrators and civil society advocates. And it is time for Tokyo to press its partners in Tehran to prosecute those who are responsible for gross human rights violations against the Iranian people.

Faraz Sanei is a Researcher with Human Rights Watch's Middle East and North Africa division.