European Council President Charles Michel is "closely engaged" with the leaders of both countries, according to an EU official.
The European Union has for a "cessation of hostilities" between Armenia and Azerbaijan after several soldiers were reportedly killed during renewed clashes in the separatist region of Nagorno-Karabakh.
The flare-up of tensions between the two countries took place "around the Lachin corridor and other places along the Line of Contact," a statement from the EU's External Action said on Wednesday.
European Council President Charles Michel is meanwhile "closely engaged" with the leaders of both countries and has spoken with Armenian Prime Minister Nikol Pashinyan, an EU official said on Thursday. He will speak to Azerbaijani President Ilham Aliyev "soon".
"His team and the EU Special Representative Toivo Klaar have been in intense contact with both sides over the past days, to push for immediate de-escalation and progress on all agenda items on the table via dialogue," the official added.
The two countries have blamed each other for the latest tensions. The Azerbaijani Defence Ministry said one of its servicemen "died of a bullet wound" during the clashes while Armenia's PM Pashinyan said on Thursday that two of his country's servicemen "were killed."
Armenia and Azerbaijan fought a violent war in the 1990s after the collapse of the Soviet Union over control of the disputed Nagorno-Karabakh region -- a mountainous territory nestled between the two countries -- in which an estimated 30,000 people died.
A six-week flare-up of tensions in 2020 led to an estimated 6,500 deaths and ended after a Russian-brokered ceasefire agreement under which Armenia ceded large parts of Nagorno-Karabakh.
Moscow also deployed some 2,000 soldiers it says are on a peacekeeping mission.