The German Foreign Ministry on Monday called on Iranian authorities and anti-government protesters to refrain from violent acts, a day after 10 people were killed in clashes with security forces across the country.

The plea from Germany's top diplomat Sigmar Gabriel came as fresh demonstrations broke out in the Iranian capital of Tehran as night fell on Monday, despite Iranian President Hassan Rouhani having vowed that authorities would deal with "rioters and lawbreakers."

Read more: Protests in Iran: The genie is out of the bottle

Read more: Iran warns of crackdown as 200 protesters arrested

The Foreign Ministry in Berlin, citing Gabriel, posted on Twitter: "We appeal to the Iranian government to respect the demonstrators' rights to freely and peacefully speak their voice. Following the confrontations in recent days, it is increasingly important that all sides refrain from violence."

The EU urged Iran to guarantee the protesters' right to "peaceful demonstration and freedom of expression," saying it will continue to monitor the situation.

US President Donald Trump also weighed in on the escalating crisis in Iran on Monday, posting on Twitter that it was "time for a change" in the country. "The great Iranian people have been repressed for many years," Trump tweeted. "They are hungry for food & for freedom. Along with human rights, the wealth of Iran is being looted."

Reports: One officer killed

According to an Iranian police spokesman on Monday, one police officer was shot dead and another three were wounded shortly after Monday night's protests erupted.

"A rioter took advantage of the situation in the city of Najaf Abad and fired shots at police forces with a hunting rifle," Iranian state television quoted a police spokesperson of saying. "As a result, three were wounded, and one was martyred."

Read more: Iran's Rouhani: We accept protesters' anger over economy

It marks the first reported security force fatality since anti-government protests broke out in the second city Mashhad last Thursday.

Although the Iranian government has imposed strict restrictions on reporting out of the country, a number of semi-official news agencies reported late on Monday that a heavy police presence lined the streets of Tehran, as small groups of protesters were seen running and chanting slogans denouncing Rouhani and his regime.

Watch video 01:51 Iranian authorities threaten to come down hard on protesters: Eric Randolph (AFP) from Tehran

Rouhani downplays unrest

Earlier on Monday, Rouhani tried to play down Sunday's violent unrest, dismissing it as "nothing."

In a statement published on the Iranian government's website Monday, the Iranian president said: "Our nation will deal with this minority who chant slogans against the law and people's wishes and insult the sanctities and values of the revolution."

The rallies are some of the largest in the Islamic Republic since a series of nationwide anti-government protests broke out following the country's disputed 2009 presidential election.

Many protesters have complained that the reforms promised by Rouhani have failed to significantly improve the economy since he took office in 2013.

Watch video 00:37 Rouhani: 'Criticizing and protesting should be done constructively'

dm/tj (Reuters, dpa, AFP)