United Nations Secretary General Ban Ki-Moon on Saturday said he is in contact with regional and international leaders and is working with UN-Arab League joint special envoy Kofi Annan to push for a peaceful solution to Syria.

After meeting with Croatian President Ivo Josipovic here in Brijuni, Croatia, Ban expressed his concerns about the situation in Syria at a joint news conference, and said the UN had remained actively engaged and fully mobilized.

The UN chief is sending Undersecretary General for Peacekeeping Operations Herve Ladsous to Syria to assess the situation.

According to Ban, the UN Security Council's decision to extend an observers' mission in Syria by 30 days was a "constructive sign."

"Now the council must redouble its efforts to forge the united way forward and exercise collective responsibility under the charter of the United Nations," he said.

The UN chief urged all parties in Syria to "stop armed violence without any conditions."

For his part, Croatian President Josipovic said Croatia fully supported all the efforts of the UN Secretary General that were aimed at finding a political and peaceful solution to the Syrian situation.