Iran on Saturday rejected "false accusations" by the UN rights chief on protests over water shortages in the country's southwest, where at least four people have been killed since last week.

UN rights chief Michelle Bachelet on Friday had asked Iran to address the chronic water shortage in Khuzestan, Iran's main oil-producing region and the wealthiest of the country's 31 provinces, instead of cracking down on protesters.

"Shooting and arresting people will simply add to the anger and desperation," she said, adding that the "catastrophic" situation had been building up for many years.

Khuzestan has been gripped by drought since March, with protests erupting in several towns and cities since July 15

Iranian media and officials have said at least three people have been killed, including a police officer and a protester, accusing "opportunists" and "rioters" of shooting at demonstrators and security forces.

State television said a fourth person was killed on Thursday and two wounded during "rioting" in the western province of Lorestan, where it said people had taken to the streets "on the pretext of the water problems in Khuzestan".

Iran's foreign ministry spokesman Saeed Khatibzadeh said Saturday that Bachelet's comments "on the recent events in Khuzestan (are) regrettable", decrying "false accusations and incorrect information".

The rights chief had failed to consider the government's "great efforts" to "relieve the suffering of the population", Khatibzadeh said in a statement, adding that this demonstrated the "political" character of the declaration.

President Hassan Rouhani on Saturday said that "despite the action, certain problems in Khuzestan province must still be quickly resolved", adding that people had "the right to protest" against the situation.

Human rights groups abroad have accused Iran of using unlawful and excessive force to quell the Khuzestan protests and have cited a higher death toll than that reported by Iranian media.