The UN special representative for Iraq, Jan Kubis, on Wednesday urged "the authorities to avoid using disproportionate, lethal force against the demonstrators."
Kubis, in his statement, also called on the authorities to "investigate and hold accountable those responsible for the outbreak of violence", Presstv Reported.
The Iraqi authorities said in a news conference on Wednesday that security personnel were injured in Tuesday's clashes.
"Thirty members of the security forces were wounded by grenades and incendiary objects being thrown," said General Jamil al-Shammari, who is in charge of security operations in Basra.
Basra is an important hub for oil exports, which account for over 95 percent of Iraq’s government revenues. Long neglected, the city is one of the few cities in the Middle East without an effective water treatment system. State officials blame a public funding crisis caused by years of low oil prices.
The city has been hit by protests against poor public services since early July.
Kubis also urged the Baghdad government "to do its utmost to respond to the people's rightful demands of clean water and electricity supplies as a matter of urgency."
Iraqi Prime Minister Haider al-Abadi said in his weekly news conference in Baghdad on Tuesday that he had ordered "no real bullets ... to be fired, in the direction of protesters or in the air."
Iraqi cleric Muqtada al-Sadr, whose coalition won the largest number of seats in Iraq's parliamentary elections, said in a tweet that "vandals infiltrated" the demonstrators.