Turkish riot police launched round after round of tear gas against protesters 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.

Turkey’s main stock exchange dropped 10.5 percent 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.

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.

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 about 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.

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.

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

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.