Georgia's rebel region of Ajaria has said its people are armed and ready to defend themselves after Georgia imposed a blockade to bring it under control.
Mr Saakashvili wants to be able to travel through Ajaria
A senior official said the authorities would defy sanctions imposed on the territory after it refused entry to
Georgian leader Mikhail Saakashvili.
Mr Saakashvili responded by closing borders and shutting off its air space.
Jemal Gogitidze said the region's authorities would not allow the borders and ports to remain closed.
The mayor of Moscow, Yuri Luzhkov, is visiting the semi-autonomous region to back President Aslan Abashidze, who is a traditional ally of Russia and has called for Russia's support.
Moscow also supported two other rebellious Georgian regions, Abkhazia and South Ossetia, that broke away in the early 1990s.
Mr Luzhkov blamed the central Georgian government for heightened tensions in the region.
Ajaria depends on income from transited goods across its territory
Its port ships around 200,000 barrels of oil a day
Ajaria has run its own affairs, withholding tax payments from central government in Tbilisi
President Saakashvili ordered the sanctions after Ajaria failed to meet a deadline on Monday evening to recognise Georgian authority.
The Georgian government has also frozen senior officials' bank accounts, and is preventing oil tankers from using its Black Sea port, Batumi.
He said the sanctions were "very temporary", but admitted they could disrupt shipments of around 200,000 barrels of oil per day from Kazakhstan and Turkmenistan that leave via Ajaria's port capital of Batumi.
Although the Georgian military was put on alert, he reassured the international community that he did not intend to unleash an armed conflict in Ajaria.
"We have enough leverage short of use of force to do things," he told reporters.
Mr Saakashvili said he wanted to visit Ajaria to drum up support for a general election on 28 March.
The election is a rerun of a poll last November which was widely recognised as rigged. Anger brought about a popular revolt, led by Mr Saakashvili, against veteran leader Eduard Shevardnadze.
Mr Saakashvili won a landslide presidential election in January.
Mr Abashidze says Georgia's new leadership will use the March election to oust him from power.
The US is keeping a close eye on events in the region, says the BBC's Chloe Arnold in the Georgian capital, Tbilisi.
Washington has thrown its weight behind a multi-billion-dollar oil pipeline through the troubled region.
US officials said Secretary of State Colin Powell had spoken to Mr Saakashvili and urged him "not to allow the situation in Ajaria to escalate".
Solomon Passy, chairman of the Organization for Security and Co-operation in Europe (OSCE) said he had met Mr Saakashvili and urged both sides to exercise caution.
"This is temporary tension which is reversible," said Mr Passy, also Bulgaria's foreign minister.