Large numbers of troops and police are enforcing a state of emergency in Georgia's capital Tbilisi, following clashes with opposition protesters.
All rallies in the country are banned and only state TV can broadcast news.
President Mikhail Saakashvili imposed the 15-day emergency after six days of opposition rallies. He said "Russian special services" had fomented unrest.
The pro-Western president has rejected the protesters' accusations of corruption and says he will not quit.
The nationwide state of emergency was declared late on Wednesday after police used tear gas, water cannon and batons to disperse thousands of protesters near the parliament building in Tbilisi.
Some 500 people sought medical treatment, most for the effects of tear gas, Georgian officials said.
The US later called for calm and for the Georgian government and opposition leaders to negotiate.
The EU foreign policy chief, Javier Solana, urged restraint from both sides, saying "political differences should be resolved within the democratic institutions".
Hundreds of interior ministry troops and also police were deployed near the parliament building on Thursday.
Police and troops have cordoned off parts of central Tbilisi
They are patrolling the capital's main thoroughfare, Rustaveli Avenue, which was the site of Wednesday's clashes.
The opposition says it has now suspended its protests and is calling on Western governments to put pressure on President Saakashvili, the BBC's Matthew Collin reports from Tbilisi.
The state of emergency was initially announced in Tbilisi for 48 hours, but that was later extended to the whole country for 15 days.
Announcing the measure, Prime Minister Zurab Nogaideli said a coup attempt had been made in the country and "we had to react to that".
Earlier, President Saakashvili said his country faced "a very serious threat of unrest".
28 Sep: Thousands rally in Tbilisi against President Saakashvili after arrest of his former ally and ex-defence minister Irakli Okruashvili
2 Nov: About 50,000 attend anti-Saakashvili rally outside parliament, calling for early elections and for Mr Saakashvili to quit
7 Nov: Riot police use force to disperse protesters after six days of opposition rallies, Mr Saakashvili imposes state of emergency
"High-ranking officials in Russian special services are behind this," he said, adding that he had evidence.
He said several Russian diplomats would be expelled from Georgia for engaging in "espionage".
Georgia's ambassador to Moscow has also been recalled for "consultations".
The Kremlin has called his allegations irresponsible and said any expulsion of Russian diplomats would be followed by an "adequate response".
On Wednesday, police used force to disperse protesters who had tried to occupy Rustaveli Avenue.
Imedi TV, which has broadcast statements by opposition leaders, stopped broadcasting on Wednesday, after riot police entered its premises.
The protesters say the police response demonstrates Mr Saakashvili's authoritarian tendencies but police said they had to unblock the capital's main road.
Protesters have been gathering outside parliament every day since Friday, when 50,000 people attended the largest street protest seen since the 2003 "Rose Revolution" that brought Mr Saakashvili to power.
"If democracy is about peaceful demonstrations, then this government has shown what kind of democracy it's practising," opposition leader Salome Zurabishvili said.
The protesters accuse Mr Saakashvili of corruption and of not doing enough to tackle poverty.
They are calling for his resignation and a fresh election.