President Donald Trump and his administration are disappointed in the European Union for not doing more to support Iran's anti-government protesters, US Secretary of State Rex Tillerson has said.

The comments from the country's top diplomat come despite the EU's stated support for Iranian citizens' right to peaceful protest, with the bloc calling only for the end to violence from both sides.

While some individual European countries have joined the US in explicitly backing the protesters, Mr Tillerson lamented a perceived lack of similar support from the 28-nation union.

"We're disappointed that the European Union has not taken a more definitive stance in supporting those voices in the country that are calling for reform," he said.

There have been 21 deaths and more than 1,000 arrests as a result of the protests so far, which erupted in Iran's second largest city Mashhad on 28 December and spread across the country.

Mr Trump has thrown his weight behind the protesters' attempt to "take back their corrupt government", pledging "great support" at the "appropriate time" in a tweet.

Despite Mr Tillerson's comments, the European Union said it was "closely following the ongoing demonstrations in Iran, the increase in violence and the unacceptable loss of human lives".

"For the EU, human rights have always been a core issue in our relationship with Iran," read a statement.

"Peaceful demonstration and freedom of expression are fundamental rights that apply to every country, and Iran is no exception.

"In the last few days, we have been in touch with the Iranian authorities. In the spirit of frankness and respect that is the basis of our relationship, we expect all concerned to refrain from violence and the right to expression to be guaranteed, also in light of the statements made by the Iranian Government."

Iran protests – in pictures Show all 11 1 /11 Iran protests – in pictures Iran protests – in pictures University students at an anti-government protest inside Tehran University, 30 December 2017 AP Iran protests – in pictures A university student at a protest inside Tehran University while a smoke grenade is thrown by anti-riot Iranian police, 30 December 2017 AP Iran protests – in pictures University students at a protest inside Tehran University, 30 December 2017 AP Iran protests – in pictures University students run away from the police during an anti-government protest inside Tehran University, 30 December 2017 AP Iran protests – in pictures An image grab taken from a handout video released by Iran's Mehr News agency reportedly shows a group of men pulling at a fence in a street in Tehran, 30 December 2017 AFP/Getty Iran protests – in pictures Demonstrators gather to protest in Tehran, 30 December 2017 AP Iran protests – in pictures Iranians chant slogans as they march in support of the government near the Imam Khomeini grand mosque in Tehran, 30 December 2017 AFP/Getty Iran protests – in pictures Iranians chant slogans as they march in support of the government near the Imam Khomeini grand mosque in Tehran, December 30 2017 Iran protests – in pictures Iranian clerics take part during a state-organized rally against anti-government protests in the country, in the holy city of Qom, south west Iran, 3 January 2018 EPA Iran protests – in pictures In this photo provided by the Iranian Students' News Agency, a clergyman takes a picture of a pro-government demonstration in the southwestern city of Ahvaz, Iran, 3 January 2018 ISNA via AP Iran protests – in pictures Pro-government demonstrators gather at the Massoumeh shrine in Iran's holy city of Qom, some 130 kilometres south of Tehran, 3 January 2018 AFP/Getty

The protests are made up mostly of working class citizens under the age of 25 who are said to be angry at government corruption, a stagnant economy and rising food prices.

Experts also believe discontent has been on the rise since the nuclear deal with the P5+1 in 2015, with many in Iran of the belief that there has been an unfair distribution of benefits throughout the population since the lifting of sanctions.

The P5+1 includes the five permanent members of the UN Security Council - the US, the UK, Russia, China and France - and Germany.

The President has been a vocal critic of the P5+1 deal which was negotiated by his predecessor Barack Obama and some observers think he might use the unrest in Iran to follow through on one of his campaign promises and tear it up.

Mr Trump has sent mixed messages about the European Union in the past.

In July 2017, the President took to Twitter to criticise the EU for being "very protectionist with the US" and said that it had to "stop". This came after he claimed to be working on a "major trade deal" with the UK.

And in January 2017 during an interview with Michael Gove he praised the UK's Brexit decision and predicted the EU would continue to break apart as a result of the refugee crisis.

However, a month later in February Trump hailed the EU as "wonderful" and said that he is "totally in favour of it".