European Union foreign policy chief Catherine Ashton urged Iran on Tuesday to refrain from using force against protesters and to respect the right to demonstrate peacefully.
Ashton "is closely following the events taking place in Iran, notably the apparent restrictions placed on the freedom of movement of certain members of the opposition and the protests taking place on the streets today," her office said in a statement.
"She calls on the Iranian authorities to fully respect and protect the rights of their citizens, including freedom of expression and the right to assemble peacefully, These are fundamental rights which need to be fully respected," it said.
"She calls on the Iranian authorities to refrain from the use of force against peaceful demonstrators."
An outlawed Iranian opposition group Tuesday angrily denied allegations that its members were responsible for shooting dead a protestor during anti-government demonstrations in Tehran.
"These lying allegations which do not fool anyone were fabricated by the regime," said the Paris-based National Council of Resistance of Iran, in a statement released in French.
"Everyone knows that it is those in power who crushed the demonstrators, firing live rounds at them and tear gas," added the council, which includes the People's Mujahedeen Organisation of Iran (PMOI), an outlawed opposition group.
Thousands of opposition supporters took to the streets of the Iranian capital on Monday. Violent clashes ensued in which riot police fired tear gas and paintballs at demonstrators, witnesses and websites said.
Ahmad Reza Radan, deputy police chief of Iran, was quoted by the FARS news agency as blaming the PMOI for shooting in which he said one protester died and nine members of the security forces were injured.
The National Council of Resistance said the PMOI was being blamed in order to justify "more executions of relatives" of its members. It said two members were executed for taking part in major anti-government protests in 2009.