Turkish riot police launched round after round of tear gas against protesters on Monday, the fourth day of violent demonstrations, as the president and the prime minister staked competing positions on the unrest.

Prime Minister Recep Tayyip Erdogan rejected the protesters' demands that he resign and dismissed the demonstrations as the work of Turkey's opposition. President Abdullah Gul, for his part, praised the mostly peaceful protesters as expressing their democratic rights.

The two men could face off next year in Turkey's presidential election.

Turkey has been rocked by violent demonstrations since Friday, when police launched a pre-dawn raid against a peaceful sit-in protesting plans to uproot trees in Istanbul's main Taksim Square. Since then, the demonstrations by mostly secular-minded Turks have spiraled into Turkey's biggest anti-government disturbances in years.

Clashes continued late into the night Monday in both Istanbul and Ankara.

In Istanbul, the country's largest city, acrid clouds of tear gas billowed up from the streets of the Besiktas area as protesters ran for cover. Riot police deployed water cannons to keep demonstrators back.

An uneasy calm settled on the city's Taksim Square, which protesters were protecting with makeshift barricades using battered buses, cars and any other material they could find to prevent police from entering the square.

In Ankara, protesters chanted for Erdogan to resign.

Turkey's main stock exchange dropped 10.5 per cent Monday as investors worried about the destabilizing effect of the demonstrations.

The Turkish Doctors' Association said one protester died after a vehicle slammed into a crowd in Istanbul but the governor's office insisted the man's death was accidental. The doctors' group also said eight people hurt in Ankara were in critical condition.

PM rejects comparison to Arab Spring

The protests are seen as a display of frustration with Erdogan, whom critics say has become increasingly authoritarian. Many accuse him of forcing his conservative, religious Islamic outlook on the lives of secular Turks.

Prime Minister Recep Tayyip Erdogan played down the plunge of the country's stock exchange on Monday. (Associated Press)

Erdogan rejects the accusations, insisting he respects all sections of Turkish society and has no desire to infringe on different lifestyles. He has also rejected accusations of being authoritarian, saying: "I am not a master but a servant" of the people.

But he does believe the protests have a deeply political purpose.

"The protests weren't about the squares or the trees, some parties were not happy about results of the elections," Erdogan said late Monday while on a visit to Morocco. "The situation is a lot calmer now and reason seems to be prevailing. I think things will return to normal. These demonstrations are not all over Turkey, just in some big cities."

In Washington, the Obama administration voiced concern Monday over Turkey's crackdown on protesters, urging authorities to exercise restraint and all sides to refrain from violence.

Secretary of State John Kerry, who has traveled to Turkey three times since becoming America's top diplomat, said the U.S. was following the situation closely and was troubled by reports of excessive force by the police. He also said Washington is "deeply concerned" by the large number of people who have been injured.

"The United States supports full freedom of expression and assembly, including the right of people to peaceful protest, because that is fundamental to any democracy," Kerry told reporters at the State Department. He maintained that his comments were not intended as interference in Turkey's internal affairs, but rather an honest expression of the importance the United States places on such values in all countries.

Erdogan, in power since 2003 after winning three elections in landslides, will hit his term limit as prime minister and could run against Gul next year. Erdogan has also advocated a new system that would give the head of state increased powers, leading to criticism that he may be trying to monopolize power.

The two men were close allies and among a core group who founded Erdogan's Islamic-rooted Justice and Development party in 2001 but there have been signs of growing differences between them. Last year, Erdogan openly criticized Gul, saying Turkey cannot have a "double-headed government" after the president called on police to halt a crackdown on a pro-secular rally. Both men have denied allegations of a rift, however.

Local media said as many as 500 people were detained overnight Monday after police clashed with more militant protesters and then moved in to break up several thousand people demonstrating peacefully. (Umit Bektas/Reuters)

An opinion poll last year indicated that Turks would vote for Gul, rather than Erdogan, in the elections.

On Monday, the leader of Turkey's secular, main opposition party discussed the protests with Gul.

"The prime minister should apologize to protesters... We hope that once he does that the incident will be over completely," Kemal Kilicdaroglu, who heads the Republican People's Party.

Gul was scheduled to meet Tuesday with Deputy Prime Minister Bulent Arinc, who is acting prime minister in Erdogan's absence.

Erdogan's adviser, Yalcin Akdogan, suggested the protests were an attempt to harm the prime minister's image.

"(Erdogan) is a leader who appears once every 100 years. He is a leader who has transformed Turkey," Akdogan said. "We won't allow him to be harmed."

On Monday, Erdogan angrily rejected comparisons with the current protests and the Arab Spring uprisings that toppled governments in Tunisia, Libya and Egypt.

"We already have a spring in Turkey," he said, alluding to the nation's free elections. "But there are those who want to turn this spring into winter.

"Be calm, these will all pass," he said.

Erdogan also played down the drop in the markets, saying: "It's the stock market, it goes down and it goes up. It can't always be stable."

Appearing defensive and angry, he lashed out at reporters who asked whether the government had understood the protesters' message.

"What is the message? I want to hear it from you," Erdogan retorted.

Gul said democracy was more than just going to the ballot box.

"Democracy does not mean elections alone. There can be nothing more natural for the expression of various views, various situations and objections through a variety of ways besides elections," he said. "The views that are well-intentioned have been read, seen and noted and the messages have been received."

When asked in Morocco about Gul's comment that democracy is more than elections, Erdogan retorted, "I don't know what the president said, but for me democracy is all about the ballot box."

The Dogan news agency said up to 500 people were detained in Ankara on Monday, and Turkey's Fox television reported 300 others were detained in Izmir, Turkey's third-largest city.

Social media was awash with reports and videos of police abuse. Turkey's Human Rights Foundation claimed more than 1,000 protesters were subjected "to ill-treatment and torture" by police.

Authorities said police excesses would be investigated, but they appeared to continue unabated. Fox showed footage of police telling one group by a building to come out, reassuring them that nothing would happen, then shooting a gas canister at them.

Turkish television stations have been criticized for providing very limited coverage of the protests, with media moguls apparently wary of upsetting the government. On Monday, dozens of people demonstrated in front of the Istanbul offices of private NTV television.

Another group of protesters drove a large bulldozer in Istanbul toward police water cannons, Dogan video showed. Medics were seen tending to the injured.

A trade union confederation called for a two-day strike starting on Tuesday.

Erdogan also blamed the protest on "internal and external" groups bent on harming Turkey and said the country's intelligence service was working to identify them.

Iraq worried about situation in Turkey

In neighboring Iraq, Prime Minister Nouri al-Maliki said on his website that his government was worried about the security implications of the situation, saying Turkey was "an essential part of the stability of the region."

Protesters run for cover during clashes with riot police near Taksim Square in Istanbul on Monday. (Kostas Tsironis/Associated Press)

"We believe that resorting to violence will widen the circle (of violence) ... in the region, and we call for restraint," he said.

Iraq and Turkey share a long, mountainous border and Iraq is home to an ethnic Turkomen minority.

The two countries' relationship has been increasingly strained over growing Turkish ties to Iraq's largely autonomous northern Kurdish region, and over Turkey's support for the Sunni rebels fighting to topple the Syrian regime.

The two-year Syrian civil war has already killed at least 70,000 people and sent hundreds of thousands fleeing the country.

US urges restraint

The Obama administration voiced concern Monday over Turkey's crackdown on protesters and urged authorities to exercise restraint and all sides to refrain from violence.

The White House said the United States believes the vast majority of those protesting have been peaceful, law-abiding citizens. Presidential spokesman Jay Carney called them ordinary citizens exercising their rights to free expression.

But Carney also said that all democracies have to work through issues, adding that Washington is concerned about Turkey's response to protesters but expects the U.S. ally to work through the issue while respecting its citizens' rights.

Police in Turkey have used tear gas for a fourth day to disperse demonstrations that grew out of a sit-in to prevent the uprooting of trees at Istanbul's main square.

Carney said the U.S. has concerns about excessive use of force and he called for the events to be investigated.

Secretary of State John Kerry, who has travelled to Turkey three times since becoming America's top diplomat, said the U.S. is following the situation closely and is troubled by reports of excessive force by the police. He also said Washington is "deeply concerned" by the large number of people who have been injured.

Kerry also said the U.S. ambassador to Turkey had conveyed those messages directly to Turkish officials.

"The United States supports full freedom of expression and assembly, including the right of people to peaceful protest, because that is fundamental to any democracy," Kerry told reporters at the State Department. He maintained that his comments were not intended as interference in Turkey's internal affairs, but rather an honest expression of the importance the United States places on such values in all countries.

"We are concerned by the reports of excessive use of force by police," he said at a joint news conference with the visiting foreign minister of Poland. "We obviously hope there will be a full investigation of those incidents and full restraint from the police force with respect to those incidents. We urge all people involved ... to avoid any provocations or violence."

Greeks rally to support Turkish protests

About 2,000 protesters chanting "Greece, Turkey, Solidarity" have staged a peaceful march to parliament in central Athens in support of the anti-government demonstrations in neighboring Turkey.

Most people who joined Monday's march were supporters of the Greek Communist Party, KKE, with many waving red party banners. Several hundred people from other protest groups took part in the rally from the Turkish Embassy to the capital's main Syntagma Square.

Lawmaker Panayiotis Lafazanis of Greece's left-wing main opposition party, Syriza, called the Turkish protests "a hopeful message for all people in the region" to resist policies that drove large sections of their societies into poverty.

Anti-austerity protests have eased over the past year in recession-battered Greece, despite an ongoing and painful austerity program implemented in exchange for international bailout loans.