ISTANBUL (AFP) - Clashes re-erupted in Turkish cities Monday as Prime Minister Recep Tayyip Erdogan shrugged off mass protests against his Islamic-rooted government that have left at least one man dead.

Despite facing the fiercest challenge to his rule since he came to office in 2002, with protestors hurling stones and burning cars, Mr Erdogan left Turkey earlier Monday on an official visit to Morocco, where he insisted the situation in his country was "calming down".

He earlier rejected talk of a "Turkish Spring" uprising by Turks who accuse him of trying to impose Islamic reforms on the secular state.

Riot police fired tear gas to disperse thousands of protestors massing near his Istanbul office and the nearby stadium of Besiktas football team late Monday as the clashes that have rocked scores of cities entered a fifth day.

As white fumes hung in the air in surrounding streets, thousands of other protestors gathered on Taksim Square, the symbolic heart of the protests.

"Tayyip, resign!" they yelled, waving red flags and banners and whistling.

Police forces also used tear gas and water cannons to disperse hundreds of protestors in the capital Ankara early on Tuesday.

Demonstrators told AFP police targeted protestors who threw stones and slabs at the security forces.

Erdogan has not flinched in the face of the protests, which he blamed on "extremists" and "dissidents" among his opponents.

"The situation is now calming down... On my return from this visit, the problems will be solved," he told a news conference in Rabat.

"The Republican People's Party and other dissidents have a hand in these events," he said, naming the main Turkish opposition.

A medics' union earlier Monday said a man was killed when a car ploughed into protestors in Istanbul on Sunday.

The unrest began as a local outcry against plans to build over Gezi Park, a rare green spot adjoining Taksim Square.

After a heavy police response it grew into wider anti-government protests in Istanbul, Ankara and other cities.

"We have had enough of the way Erdogan understands democracy and the way he wants to dictate his rules," said Mr Ozgur Aksoy, a young engineer demonstrating in Gezi Park on Monday.

Rights groups and doctors said more than a thousand people had been injured in clashes in Istanbul and 700 in Ankara.

The government's latest estimate on Sunday put the figure at 58 civilians and 115 security forces injured, with clashes in 67 cities. It also said more than 1,700 people had been arrested across the country and that many had since been released.

Mr Erdogan dismissed the protestors as "vandals", stressing that he was democratically elected.

His Justice and Development Party (AKP) has won three successive parliamentary elections, but opponents have expressed mounting concern that Turkey is moving toward conservative Islam.

- Allies worried at 'excessive' force -Echoing Britain and other Western allies of Turkey, United States (US) Secretary of State John Kerry voiced concern over "reports of excessive use of force" by Turkish police and urged all sides to "avoid any provocations or violence".

Mr Erdogan's ally President Abdullah Gul called for calm and promised protestors their voice had been heard, urging an end to the disturbances.

"I am calling on all my citizens to abide by the rules and state their objections and views in a peaceful way, as they have already done," he said.

Mr Erdogan himself has lashed out at Twitter, used by many of the protestors, accusing the online messaging service of spreading "lies".

"Society gets terrorised this way," he told the Haberturk television channel.

The AKP is traditionally backed by conservative Islamic politicians and voters in Turkey, a secular state peopled mostly by Muslims.

The wave of protests "is a result of growing frustration and disappointment among secular segments of society who could not influence politics over the last decade", said Mr Sinan Ulgen, a scholar at the think tank Carnegie Europe.

The Istanbul stock exchange closed 10 per cent lower on Monday and the Turkish lira fell against the euro and the dollar.

Turkey's Confederation of Public Workers' Unions said it would hold a two-day strike from Tuesday against what it called "state terror" by authorities against the demonstrators.

Since coming to power in 2002, Mr Erdogan has passed contested reforms on religious education and a recent law curbing the sale of alcohol. In 2004 he backed down on a proposed adultery law.

Shrugging off the rising protests, he pushed ahead on Monday with what he said was a pre-planned four-day official trip to Morocco, Algeria and Tunisia.

Speaking before his departure, he pointed to elections set for next year, when observers expect him to run for president.

Asked about the president's more conciliatory comments, Mr Erdogan again struck an intransigent note.

"I don't know what the president said, but for me, democracy comes from the ballot box."