In response, Saakashvili issued a one-day ultimatum to Adjar leader Aslan Abashidze to accept Tbilisi's authority and start disarming his paramilitary forces or risk a blockade and economic isolation.
"Either we now will all stand together and once and forever put a curb on banditry, feudalism, and treason in Georgia -- I can't call it otherwise, this is treason -- or we will stop existing as a state. And Georgia will disappear. But I must warn you that nobody will be able to do this during my presidency," Saakashvili said.
Saakashvili said air, land, and sea routes to Adjaria would be blocked and that authorities would move to freeze foreign bank accounts belonging to Adjar officials. He stressed, however, that the problems must be resolved peacefully.
Abashidze, in response, today imposed a curfew.
International efforts are now under way to diffuse the crisis.
The Organization for Security and Cooperation in Europe (OSCE) has called on both sides to exercise restraint and use all available means to resolve differences peacefully.
OSCE spokesman Richard Murphy told RFE/RL that the current OSCE chairman, Bulgarian Foreign Minister Solomon Passy, was in Tbilisi and was to meet with Saakashvili.
"The OSCE is concerned about the apparent increase in tension, at least as far as language is concerned, and our chairman-in-office, Bulgarian Foreign Minister Solomon Passy, who is in Georgia at the moment...[is] appealing to all sides to exercise restraint and to use all means to resolve their differences peacefully," Murphy said.
Russia, which has a military base in the Adjar capital of Batumi and has been a traditional supporter of the Adjar leadership, has warned Tbilisi against the use of force. Foreign Ministry spokesman Alexander Yakovenko has said all responsibility for a crisis would rest with the Georgian leadership.
Turkish Foreign Minister Abdullah Gul today said Turkey supports Georgia's territorial integrity. He said "Adjaria is part of Georgia and stability in the Caucasus is in the interest of Turkey and the region."
Saakashvili put the Georgian military on alert yesterday after he and his convoy were prevented from entering Adjaria for a campaign appearance ahead of Georgia's parliamentary elections later this month (28 March).
Reports say Georgian armored personnel carriers could be seen near the Adjar border, and Adjar television reported that Georgian forces and heavy weapons were concentrated near Poti.
Georgian news reports say guns have been handed out to Abashidze supporters. Abashidze, who returned to Adjaria from Moscow early today, said he was ready to discuss Saakashvili's demands.
Speaking on Adjar television, Abashidze said he and Saakashvili had "a difficult conversation" on the telephone last night. Abashidze said Saakashvili had demanded control of customs duties from Adjaria, which borders Turkey, and of the port in Batumi.
Saakashvili has made uniting the country a key goal since coming to office in January. But the escalating tensions have generated fears of hostilities like those that led to wars in Abkhazia and South Ossetia, two rebellious provinces that broke away from Georgia in the early 1990s.
Abashidze today, in an interview with Batumi TV, warned that Saakashvili's actions could lead to Adjaria's split from Georgia.
"On the grounds of mistakes made by one president [Zviad Gamsakhurdia], we lost South Ossetia. The second president [Eduard Shevardnadze] completed this process and we finally lost South Ossetia. He also lost Abkhazia. The third president goes in the same direction and now Adjaria is in focus," Abashidze said.
Georgian analyst Archil Gegeshidze, of the Tbilisi-based Foundation for Strategic and International Studies, says a confrontation between Abashidze and Saakashvili was probably inevitable.
"This is perhaps the first case when Saakashvili, being the president of Georgia, has encountered [such a] difficult task. Of course, this was to be predicted that the confrontational clash between the government and the Adjar leadership would occur because the central government, the values, the intentions with which this new central government has come to power and the values and the business practices of the Adjar leadership are totally incompatible," Gegeshidze said.
Gegeshidze says that as the 28 March parliamentary elections approach, he expects the tensions to escalate. He told RFE/RL that Abashidze may fear that free and fair elections could lead to him losing power.
"They [the government] hope that if there are free and fair elections in Adjaria, then the authority of Aslan Abashidze would be seriously undermined in Adjaria. So they are insisting, they are making efforts in order to ensure that the elections in Adjaria are as transparent and as democratic as possible. That's why Saakashvili was trying yesterday to enter Adjaria to meet the people, to find out what is the real support for the local government, the local leader, and this of course would be very dangerous for the local leadership. That's why they did their best not to allow Saakashvili to enter Adjaria," Gegeshidze said.
Gegeshidze says if Abashidze is really that unpopular, there may be only two options left for the Adjar authorities: either not to hold elections at all or to hold elections that they can control.