Civilians killed in clashes between Armenia and Azerbaijan in disputed region

What's happening: Armenia said Azerbaijan conducted air and artillery attack on the disputed region, which Azerbaijan claimed was in response to Armenian shelling, per Reuters.

• Armenia declared martial law and mobilized its male population on Sunday. Authorities in Nagorno-Karabakh have also declared martial law.
• Human rights activists in Armenia said at least two civilians have been killed by Azerbaijani shelling, while officials in Azerbaijan reported an unspecified number of civilian deaths and six wounded. Reuters could not independently confirm the deaths.

What they're saying: Turkey's President Recep Tayyip Erdoğan pledged support for Azerbaijan and called Armenia "the biggest threat to peace and tranquillity in the region," according to the BBC.

• Russia, which has acted as a mediator in the conflict and arms supplier to both sides, called for a ceasefire and talks to cool the situation.
• The U.S. issued a statement on Sunday afternoon condemning the violence and calling on the two sides to return to negotiations to halt escalation. "The United States believes participation in the escalating violence by external parties would be deeply unhelpful and only exacerbate regional tensions," a State Department spokesperson said.