ISTANBUL — Turkey's government on Wednesday offered a first concrete gesture aimed at ending nearly two weeks of street protests, proposing a referendum on a development project in Istanbul that triggered demonstrations that have become the biggest challenge to Prime Minister Recep Tayyip Erdogan's 10-year tenure.

Protesters expressed doubts about the offer, however, and continued to converge in Taksim Square's Gezi Park, epicenter of the anti-government protests that began in Istanbul 13 days ago and spread across the country. At times, police have broken up demonstrations using tear gas, water cannon and rubber bullets.

The protests erupted May 31 after a violent police crackdown on a peaceful sit-in by activists objecting to a development project that would replace Gezi Park with a replica Ottoman-era barracks. They then spread to dozens of cities, rallying tens of thousands of people each night.

In a skirmish late Wednesday in Ankara, police used tear gas and water cannon to break up some 2,500 protesters who set up makeshift barricades on a road leading to government offices.

The referendum proposal came after Erdogan, who had been defiant and uncompromising in recent days, met with a group of 11 activists, including academics, students and artists, in Ankara. However, groups involved in the protests in Taksim and the park boycotted the meeting, saying they weren't invited and the attendees didn't represent them.

Greenpeace said it didn't participate because of an "environment of violence" in the country, while Taksim Solidarity, which has been coordinating much of the occupation of Gezi Park, said it had not been invited. The group reiterated its demands that Gezi remain a public park, that abusive senior officials be fired, and all detained protesters be released — not issues the referendum would address.

But the discussion was the first sign that Erdogan was looking for an exit from the showdown, and came hours after some European leaders expressed concern about recent strong-armed Turkish police tactics and hopes that the prime minister would soften his stance.

Huseyin Celik, spokesman for Erdogan's Islamic-rooted Justice and Development party, announced it would consider holding a referendum over the development project. But he said any vote would exclude the planned demolition of a cultural center that the protesters also oppose, insisting it was in an earthquake-prone area and had to come down.

In a more defiant note, he said the ongoing sit-in in Gezi Park would not be allowed to continue "until doomsday" — a sign that authorities' patience is running out. But Celik also quoted Erdogan as saying that police would be investigated, and any found to have used excessive force against protesters would be punished.

Erdogan, who has claimed the protests were orchestrated by extremists and "terrorists," has become the centerpiece of the protesters' ire. So a referendum would be a political gamble that the government can mobilize its supporters, win the vote and the demonstrators would go home.

"The most concrete result of the meeting was this: we can take this issue to the people of Istanbul in a referendum. We can ask the people of Istanbul if they want it (the barracks)," Celik said. "We will ask them: 'Do you accept what's going on, do you want it or not?'"

But many protesters were skeptical.

"I don't think anything changed with that," said Hatice Yamak of the referendum plan. "We don't think he will do it — I think he's lying."

Other protesters were suspicious of how the vote would be held.

"I think there will be a referendum but it won't be fair," said Mert Yildirim, a 28-year-old who had been attending the protests every night. "They will announce that the people want Gezi Park to become a shopping mall. They will cheat."

But Erdogan's maneuver could prove shrewd, by putting the protesters in a position of rejecting a referendum — a quintessential exercise of democracy. Many of them have accused Erdogan, who was re-elected in 2011 and has presided over striking economic growth, of showing an increasingly authoritarian streak.

"(The referendum proposal) falls short, and it won't help. This is not the way town planning is done," said Korhan Gumus, an architect and member of the Taksim Solidarity Platform activist group. "The referendum will polarize society even more. (Gezi Park) will become a battleground."

Party spokesman Celik appeared confident that Erdogan would be vindicated at the ballot box: "We cannot predict the decision of the people, but we believe that our people will side with our party's position."

As if to let the referendum proposal sink in, the Istanbul governor, Huseyin Avni Mutlu, tweeted that riot police would not enter the park on Wednesday.

Turkish leaders were also grappling with a public image stain. International TV networks have beamed images of clashes on the square, including a muscular police sweep overnight Tuesday to Wednesday that Turkey's Human Rights Foundation said injured more than 600 people, including a 1-year-old baby.

In London, British Prime Minister David Cameron called the events in Istanbul "disturbing and concerning," while stopping short of criticizing Erdogan's response. A spokesman for Chancellor Angela Merkel said Germany's government was watching developments "with great preoccupation," and urged "de-escalation."

Over the two weeks, four people have died in the protests, including a police officer, and more than 5,000 people have been injured or sought treatment for tear gas.

The protests took a new flavor earlier Wednesday as thousands of black-robed lawyers stormed out of their courthouses to deride allegedly rough treatment of their colleagues detained by police a day earlier. Sema Aksoy, the deputy head of the Ankara lawyer's association, said the lawyers were handcuffed and pulled over the ground. She called the police action an affront to Turkey's judicial system.

"Lawyers can't be dragged on the ground!" the demonstrating lawyers shouted in rhythm as they marched out of an Istanbul courthouse. Riot police stood off to the side, shields at the ready.

A spokesman for the Canadian Broadcasting Corp. said police had detained two of its reporters covering the protests in Istanbul. Sasa Petricic and Derek Stoffel were in "good condition," CBC spokesman Chuck Thompson said. Canadian Foreign Affairs Minister John Baird called the Turkish ambassador to express his concerns.

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Keaten reported from Ankara. Suzan Fraser and Ezgi Akin in Ankara, Cassandra Vinograd in London, Juergen Baetz in Berlin, and Rob Gillies in Toronto contributed to this report.