Turkey's foreign minister arrived in Azerbaijan on Sunday for talks over the breakaway region of Nagorno-Karabakh after Baku's arch-enemy Armenia requested security assistance from Russia. 

"We are once again in Baku with our brothers to renew our strong support for dear Azerbaijan and exchange on the latest developments in Nagorno-Karabakh," Foreign Minister Mevlut Cavusoglu said on Twitter.

On Saturday, Armenian Prime Minister Nikol Pashinyan formally asked Russian President Vladimir Putin to begin consultations on security assistance, invoking the two countries' defence pact.

Pashinyan said hostilities were approaching Armenia's borders and reiterated that Turkey was backing Baku. 

Moscow's defence pact with Armenia does not extend to Nagorno-Karabakh and Russia said Saturday that "necessary" help would be provided if the fighting reaches Armenian territory.

At the same time, Russian foreign ministry spokeswoman Maria Zakharova said "concrete formats" of assistance to Armenia would be discussed.

Armenia's request for assistance from Moscow further raised fears of Russia and Turkey getting sucked into the decades-old conflict over Karabakh.

Armenia and Azerbaijan have been engaged in fierce fighting for more than a month over Karabakh, a region of Azerbaijan controlled by Armenian separatists in the wake of the break-up of the Soviet Union.

Fighting continued overnight and Sunday morning, the warring sides said.

The Karabakh separatist leadership accused Azerbaijan of striking civilian settlements including the strategic town of Shusha.

"In the morning the enemy forces renewed offensive operations," the Karabakh army said.

The Azerbaijani defence ministry for its part accused Armenian forces of targeting its army and civilian settlements on Saturday and overnight.

More than 1,200 people from both sides have been reported killed in the fighting but the death toll is believed to be substantially higher.