Fighting broke out in the early hours of Sunday between Armenian-controlled Karabakh and Azerbaijan, with Armenia declaring martial law and the total mobilization of its military.
The reports early Sunday were unclear as to how the fighting began, but it follows months of tensions after clashes in July. In recent weeks, Turkey has expressed support for Azerbaijan and rumors emerged of Turkish military flights and the recruitment of Syrian rebel militias to fight against Armenia. 
By 10:00 in the morning, reports from Karabakh indicated fighting along the “line of contact” with Azerbaijan. Nagorno-Karabakh is an area controlled by Armenia but claimed by Azerbaijan. It is one of many such areas that are the result of changes in territory in the last century, and one of many disputed areas in the post-Soviet Caucasus. It has its own self-declared Republic of Artsakh, which is Armenian. 
The leader of Artsakh told the press that there was an attack by Azerbaijan in the morning on Sunday. Reports indicated that shelling and missiles had landed near the city of Stepankert; an Azerbaijan armored vehicle was photographed on fire. Artsakh leader Arayik Harutyunan appeared dressed in fatigues, according to reports. According to the same social media reports by Emil Sanamyan, the Armenian Defense Ministry said drones had been involved in an attack on its Tavush province. Turkish media claimed that Armenia carried out “attacks against Azerbaijan.”
Speaking to The Jerusalem Post, Azerbaijan's Ambassador to the US Elin Suleymanov Emin oglu cautioned against taking Armenia's word at face value.
In a statement uploaded to Twitter, Hikmet Hajiyev, assistant of the Azeri president and head of the Foreign Policy Affairs Department of the presidential administration, said that the Armenian forces violated a ceasefire and struck densely populated civilian areas with heavy firepower in a "deliberate and targeted" attack. The statement further mentioned that there were several casualties among both civilians and military personnel, as well as heavy damage to infrastructure.
Hajiyev slammed Armenia for its "gross violation of international humanitarian law, including the Geneva Convention," and its "flagrant disregard for international law, the UN charter and the international community."
He added that Azerbaijan would respond with counter-measures in response, and warned that "The responsibility for the present situation and future developments lie squarely with Armenia's military-political leadership."

Hajiyev also uploaded pictures of the area, showing damaged infrastructure and wounded civilians.

 

Azerbaijan's Defense Ministry further said it had launched a military operation along the "contact line," a heavily-mined no-man's-land that separates the Armenian-backed forces from Azeri troops in the region, Russian news agencies reported.
 The ministry said that an Azerbaijani helicopter had been downed but that its crew had survived.
In response to the attacks, Armenia has declared martial law, and has ordered the total mobilization its military, according to a statement obtained by Reuters. Azerbaijan, however, has said there is no need for them to fully mobilize its army, as its military is fully staffed.
THE LEAD-UP to the clashes included days of rumors that Turkey was prodding Azerbaijan to do more. Ankara has promised military support for Baku. In addition, the US embassy in Azerbaijan issued a warning against travel to near the border area with Armenia.
 
The first reports of fighting emerged between 6:00 and 7:00 in the morning. These included reports of drone and missile attacks from Azerbaijan, as well as reports of Armenian mortar and artillery fire. The fighting was believed to be the heaviest since the 1990s in many areas. Armenian sources claimed to have downed helicopters and UAVs.
Azerbaijan has a large array of drones, including numerous kamikaze drones that act like cruise missiles, which it has used effectively in the past. The fact that they may be shot down is not a great loss because they are intended to be destroyed in contact with adversaries.  
At the same time, Turkey’s TRT also had a live broadcast from Azerbaijan, indicating that the country's state broadcaster may have had advanced warning of the clashes. Internet service was also restricted in Azerbaijan in an apparent effort to prevent the spread of fake news or news that might show losses at the front.
It is unclear if the attacks are a well-planned assault designed to take back parts of Nagorno-Karabakh from Armenian control or if they are more limited.
Rumors of Turkish military transports over the last 48 hours flying to Azerbaijan would indicate that Turkey wants to play a larger role. Turkey’s defense minister and president have been seeking to indicate in recent weeks that they would like to back Azerbaijan against Armenia. They have referred to Azeri soldiers as martyrs, have spoken in religious and nationalist terms about the support Ankara could give, and have also warned Armenia not to “play with fire.”
Turkish media trotted out its usual far-right line of extreme nationalists on Sunday to condemn Armenia. Turkish presidential adviser Ibrahim Kalin condemned Armenia. This appears to show Turkey’s potential involvement.
Reuters contributed to this report.