Emily Thornberry has responded to criticism over her ambivalent approach to the Iranian protesters by saying Iran had seen “clear spontaneous public outpourings that we can all understand and support”.

The shadow foreign secretary also denounced the Iranian judicial system as capable of draconian and arbitrary punishments, especially against minorities and women. She also accused Iran of escalating its proxy wars with Saudi Arabia.

Thornberry had been criticised by the Conservative MP Tom Tugendhat, the chairman of the foreign affairs select committee, after she told the BBC it was hard to tell who was wearing the white hats in Iran, remarks that led some to claim she saw a moral equivalence between the protesters and the Iranian government.

Tugendhat said it was “hardly a knee-jerk reaction” to condemn the regime, which he claimed had been brutalising women and murdering gay people for 40 years.

Jeremy Corbyn has been silent on the Iranian protests, but Thornberry says her interpretation of events in Iran is the same as the Labour leader’s. Corbyn critics claim historically he has been too close to Iran, has spoken at rallies sympathetic to the regime and overlooked its human rights abuses.

In 2014, the year before he became Labour leader, Corbyn spoke at a rally celebrating 35 years of the Iranian revolution in which he highlighted the role of the British in inspiring the 1953 coup that brought the repressive Shah to power.

In a long Facebook post attempting to clarify public understanding of her thinking, Thornberry said the situation was complex and required caution, adding it would be wishful thinking to believe regime change would automatically lead to an Iran with closer ties to the west.

She also said she “was appalled by the recent violence with several protesters reported dead and many hundreds of others awaiting an uncertain fate after being arrested. There is a particular responsibility on the Iranian authorities to show restraint in their policing to allow peaceful democratic protests and to enable a proper dialogue so that all political and economic grievances can be raised and resolved.

“Peaceful protests should never be treated as a crime and to do so will only worsen the sense of grievance among those who have taken to the streets in recent days.”

Amid reports of continuing street protests and mass arrests, Thornberry sought to distinguish different elements in the protests, including “trade unionists fighting for workers’ rights, women fighting against arcane laws governing their voting and sex lives, as well as working-class communities protesting about unemployment and the cost of living”.

At the same time she pinpointed other elements calling for the restoration of the monarchy and hardline forces inside the theocratic establishment seeking to undermine the reformist President Hassan Rouhani and exploiting public anger at food prices.

She said the west had been too quick to welcome the Arab spring in Egypt and Libya. In Syria, similarly she said: “Predictions of the strength of western-backed anti-Assad rebel forces proved as mythical as many of us had always thought.”

She said it would be easy but reckless to say: “Let’s throw our weight behind the Iranian protests even if we don’t fully understand what they are, let’s pursue the overthrow of the Iranian regime even if we do not know what will replace it.”

She added she was not prepared to indulge in wishful thinking and heroic assumptions that say pursuing regime change in Iran will automatically deliver better outcomes.