Nagorno-Karabakh, an area in the Caucasus mountains, broke away from Azerbaijan in the late 1980s which sparked a two-year war which started in 1992.
About 30,000 people were killed and about one million other forced from their homes during six years of fighting that ended with a ceasefire in 1994.
Wednesday's clashes between Armenia and Azerbaijan were one of the biggest in recent years.
Robert Kocharyan, the Armenian president, said Azerbaijan had launched the attack to take advantage of his country's tense political standoff after protests against last month's election.
|"It is possible in Azerbaijan they thought the situation in Armenia had distracted the authorities in Nagorno-Karabakh" |
Robert Kocharyan, Armenia's President
A state of emergency had been imposed after supporters of Levon Ter-Petrosian demonstrated against his defeat by Serzh Sarksyan, the prime minister who will now become the country's president.
"It is possible in Azerbaijan they thought the situation in Armenia had distracted the authorities in Nagorno-Karabakh," Kocharyan said.
Azerbaijan said Armenia was trying to distract attention from protests in Yerevan by focusing on an external enemy.
"The Armenian side resorted to provocations on the frontline in a bid to switch the attention of the international community and its own citizens from internal tensions to an external enemy," a spokesman from the Azeri foreign ministry said.
The breakaway region's foreign ministry appealed to the Organisation for Security and Co-operation in Europe to intervene and conduct crisis-monitoring in the conflict zone.
Earlier this week, Ilham Aliyev, the Azeri president, said his country was ready to take back Nagorno-Karabakh by force if need be, and was buying military equipment and arms in preparation.
Aliyev said Kosovo's newly declared independence had emboldened Armenian separatists in the mountainous enclave.
The US and Russia have urged both parties to show restraint.
However, a US official said on Wednesday that he had received assurances from both sides that they have returned to a ceasefire in the disputed territory.
Matthew Bryza, US deputy assistant secretary of state, said after a series of meetings in Azerbaijan and a telephone call with Vartan Oskanian, Armenia's foreign minister, that he was satisfied that tensions in Nagorno-Karabakh had subsided.