(Adds details, background, border closed)
ALMATY, May 26 (Reuters) - Police in Uzbekistan exchanged gunfire with a group of armed men in the eastern town of Khanabad and an explosion was heard, witnesses said on Tuesday.
The circumstances of the shooting in the small town on Uzbekistan's border with Kyrgyzstan were unclear and there was no word on casualties. Authorities in Uzbekistan, Central Asia's most populous country, could not be reached for comment.
A security source in neighbouring Kyrgyzstan confirmed the shootout and said the Uzbek authorities had closed the border.
"They are dealing with an emergency situation," the source said. "There was a shootout. Other details are being investigated."
One Khanabad resident told Reuters he had heard an explosion in the town centre overnight. He said security had been tightened but there were no signs of unrest on Tuesday.
The West is concerned about stability in Uzbekistan, a reclusive nation which lies on a new route for U.S. supplies bound for troops fighting in neighbouring Afghanistan.
Three residents of Andizhan, a city 70 km (42 miles) to the west of Khanabad which was the scene of a bloody 2005 uprising, said on Tuesday tanks had appeared on the streets and police manned most city corners.
Uzbek officials said 187 people died in Andizhan in 2005 when troops opened fire on a protest against armed Islamist militants. Independent witnesses said hundreds of unarmed civilians were killed during the uprising.
Uzbekistan has been ruled by President Islam Karimov with an iron fist since 1989. Karimov is criticised in the West for not tolerating dissent and jailing political opponents.
The Uzbek leader had been due to leave for Brazil on a visit on Tuesday but it was unclear whether he had departed.
Independent information is difficult to get in Uzbekistan which has cracked down on foreign media and local reporters since the 2005 Andizhan uprising, accusing them of bias.
The country has become increasingly isolated since the uprising and seen its command-style economy hit as remittances from migrant workers dried up with the global economic crisis, increasing the hardship of its impoverished population. (Writing by Maria Golovnina; Additional reporting by Olga Dzyubenko in Bishkek, Olzhas Auyezov in Almaty; Editing by Sophie Hares)
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