Turkey warned on Monday it may bring in the army to help quell nationwide anti-government protests, as two major union federations went on strike over police violence against demonstrators.
The presence of soldiers on the streets would mark a major escalation of a crisis that has raged for nearly three weeks, and poses the biggest challenge yet to prime minister Recep Tayyip Erdogan's Islamic-rooted government.
Police "will use all their powers" to end the unrest, deputy prime minister Bulent Arinc said in a televised interview. "If this is not enough, we can even utilise the Turkish armed forces in cities."
Turkey's trouble flared with fresh intensity after officers on Saturday evicted campers from Istanbul's Gezi Park, the epicentre of the protest movement.
Police spent the weekend firing tear gas and water cannon at thousands of angry protesters, with running battles lasting into Monday morning in Istanbul and the capital Ankara.
Turkey's two main trade unions, KESK and DISK, who represent hundreds of thousands of public sector workers, organised a one-day stoppage in protest, their second strike action since the unrest first erupted.
Groups of several hundred union members took to the streets in Istanbul, Ankara and the western city Izmir calling for the police violence to "end immediately". Their progress was at times blocked by police but there were no reports of fresh clashes.
The crisis began when a sit-in to save Gezi's 600 trees from being razed in a redevelopment project prompted a brutal police response on May 31, spiralling into countrywide demonstrations against Erdogan, seen as increasingly authoritarian.
So far four people have been killed and nearly 7,500 people injured, according to the Turkish Medical Association (TBB).
At a rally of more than 100,000 supporters of his ruling Justice and Development Party (AKP) on Sunday, Erdogan defended his response to the demos, saying it was his "duty as prime minister" to order police to storm Gezi Park after protesters defied his warnings to clear out.
He also vowed to go after those who had offered assistance to the protesters, in a nod to the luxury hotels who opened their doors to people fleeing the volleys of tear gas and jets of water during the park's evacuation.
"We know the ones who sheltered in their hotels those who cooperated with terror. They will be held accountable," he said.
Merkel 'shocked' by violence
The United States and other western allies have widely criticised Erdogan's handling of the crisis, undermining Turkey's image as a model of secular democracy.
German Chancellor Angela Merkel on Monday said the police response to the protesters "was much too harsh".
"What is happening in Turkey at the moment does not meet with our ideas of freedom of assembly, (or) freedom of expression," she said. "I am in any case shocked."
That the Turkish government has now raised the threat of deploying the army shows it is struggling to end the unrest, said professor Ilter Turan, a political scientist at Istanbul's private Bilgi University.
"The government will mobilise everything in order to halt the movement at any cost," he said. "This also indicates the government's acknowledgement that what's happening is extraordinary and that they can't control it."
Observers say Turkey's pro-secular military been steadily sidelined during Erdogan's decade in power, though some members of the gendarmerie were stationed at strategic points in Istanbul at the weekend to stop protesters from regrouping.
Opponents accuse Erdogan of forcing Islamic conservative reforms on the mainly Muslim but staunchly secular nation of 76 million, and of pushing big urban development projects at the expense of local residents.
But Erdogan, 59, has been in power since 2002 and remains popular. His AKP has won three elections in a row, taking nearly half the vote in 2011 after presiding over strong economic growth.
A survey by Metropoll, published in the Zaman daily on Monday found that the AKP would still come first if elections were held now, with 35.3 percent of the vote.
In a bid to end the row over the redevelopment of Gezi Park, Erdogan last week offered to suspend the project pending a court ruling on its legality.
But the Taksim Solidarity group, seen as most representative of the protesters, rejected the olive branch, saying their movement was now more than a conservation struggle.