Here are five facts about the country:
• Azerbaijan is an ex-Soviet republic on the Caspian Sea, sandwiched between Iran and Russia. Its roughly eight million people speak a language closely related to Turkish, and most of them are Shia Muslims.
• With an oil pipeline to the Mediterranean Sea about to come on stream, Azerbaijan is a hub for exporting Caspian Sea crude to world markets. Energy markets see Caspian oil as a valuable alternative to Russia and Saudi Arabia.
• Late president Haydar Aliyev ruled almost uninterrupted from 1969 to 2003. His son Ilham succeeded him in an election international monitors said was marred by vote-rigging and intimidation.
• One of only two Muslim states to send troops to Iraq, Azerbaijan is a US ally. Some Washington policy-makers believe Azerbaijan can be used to apply pressure on Iran, home to about 15 million ethnic Azeris.
• The Nagorno-Karabakh region, internationally recognised as part of Azerbaijan, has been controlled by Armenian separatists since a war in the early 1990s. Peace talks have been stalled for several years and the two sides' forces face each other across a tense ceasefire line.
Azerbaijan has come under criticism from human rights organisations such as Amnesty International and Human Rights Watch for detention of political opponents, stifling of freedom of expression and clampdown on journalists and civil society organisations.