The United Nations on Tuesday highlighted the impact of the Syrian conflict on Lebanon as it called for support for the country's armed forces and other key institutions.

U.N. leader Ban Ki-moon and U.N.-Arab League envoy Syria envoy Lakhdar Brahimi have stressed support for President Michel Suleiman and key state institutions as the 27-month-old Syria war increasingly spills over the border.

A battle between the army and followers of Salafist cleric Sheikh Ahmed al-Asir in the southern city of Sidon was "a stern reminder to all of the risks of the conflict in Syria spreading across the border," Brahimi said Tuesday in Geneva.

At least 17 troops were killed in the battle and the army has launched a manhunt for al-Assir. Brahimi said at least 50 people were killed in all in the worst clashes in the country since the start of the Syrian war in March 2011.

"Lebanon is a country that has a balance of power inside the country and the effects of the Syrian conflict right now obviously are having some kind of an impact there," said deputy U.N. spokesman Eduardo del Buey.

In a statement released by his office on Monday, Ban said he "stresses that all in Lebanon should fully respect the authority of the state and its institutions under the leadership of President Suleiman, in particular the Lebanese Armed Forces whose role is essential to protect all Lebanese."

Ban is following events in Lebanon with "deep concern," added the statement which condemned the attacks on the army.

"The secretary general reminds all concerned in Lebanon of their responsibility to avoid conflict and uphold the principles of mutual respect and coexistence in order to preserve Lebanon's national unity."

Suleiman has called on Hizbullah to end its role in the Syria war.

Hizbullah has taken the side of President Bashar Assad and played a key role in taking the town of Qusayr.