The European Council late Thursday failed to agree on sanctions against Russia over Syria, but warned that the EU could consider "all available options, should the current atrocities continue".
In a statement after the first day of the summit in Brussels, EU leaders strongly condemned the attacks by the Syrian regime and its ally Russia on civilians in Aleppo.
Friday's agenda for the summit include recent developments on the EU's migration policy, the security of EU borders, and cooperation with the African countries, along with relations with Russia and the situation in Syria.
The EU called on Russia and the Syrian regime "to bring the atrocities to an end and to take urgent steps to ensure unhindered humanitarian access to Aleppo and other parts of the country".
"Those responsible for breaches of international humanitarian law and human rights law must be held accountable," said the statement.
The EU also urged that all efforts be made "to extend the ceasefire, bring in humanitarian aid to the civilian population and create the conditions for opening negotiations on a political transition in Syria."
On Tuesday, Russian and Syrian warplanes ceased striking Aleppo, Syria in the run-up to the eight-hour "humanitarian pause" slated for Thursday.
Later on Thursday, Russia's defense minister announced that Russia had extended the "pause" for an additional 24 hours.
"This evening we had a broad discussion about Russia," said Donald Tusk, the European Council president. “Leaders emphasized all sorts of Russian activities, from airspace violations, disinformation campaigns, cyber-attacks, interference into the political processes in the EU and beyond.”
He added, "Given these examples, it is clear that Russia's strategy is to weaken the EU."
Tusk underlined that it was not trying to increase tensions with Russia, saying that the EU is only reacting to steps taken by Russia.
Tusk asserted that the EU is always ready to engage in dialogue.
"But we will never compromise our values or principles. That is why leaders agreed to stay the course. And above all to keep the unity of the EU," he added.