Baku - Azerbaijan on Sunday declared martial law and a curfew in capital Baku and several other cities, as fighting with Armenian rebel forces in Nagorny Karabakh claimed military and civilian casualties on both sides.

"Martial law will be introduced as of midnight as well as a curfew from 9 pm to 6 am," in Baku, several other cities and districts that are close to the Karabakh frontline, presidency spokesman Hikmet Hajiyev told journalists.

Sixteen Armenian separatist fighters were killed in Azerbaijan's breakaway region of Nagorny Karabakh after heavy fighting broke out with the Azerbaijani military on Sunday, rebel officials said.

"According to preliminary data, 16 (Karabakh) servicemen were killed and more than 100 wounded" since fighting erupted, the separatist defence ministry said, while both Baku and Yerevan reported civilian casualties earlier Sunday.