The United Nations political chief said Wednesday that the situation in Lebanon remains "fairly fragile" despite the cessation of hostilities between Israel and Hizbullah and warned about the presence of armed groups in the country.

"My main message today was that while the ceasefire has been holding, there still is a lot of work there to do," Under-Secretary-General for Political Affairs B. Lynn Pascoe told reporters after he briefed the Security Council on Secretary-General Ban Ki-moon's recent report on the implementation of Resolution 1701 which ended the Israel-Hizbullah war in 2006.

Pascoe also noted that the deadly clashes in May between pro- and anti-government gunmen, as well as fighting in the northern city of Tripoli on Wednesday, were indications of the fragile nature of the situation in Lebanon.

"We would urge them to move as quickly as possible to fulfilling the requirements of the Doha agreement," Pascoe said about the accord reached in late May which helped break Lebanon's political deadlock by paving the way for the election of a new president and the establishment of a national unity cabinet.

He said the use of heavy arms, which are banned by 1701, and the closure of roads by armed elements undermine the implementation of the resolution.

The May clashes revealed the presence of heavy weapons in Lebanon outside the control of the army, Pascoe said.

In his report, Ban expressed serious concern about the presence of "unidentified armed elements" in the area of operations of the U.N. Interim Force in Lebanon (UNIFIL), along with restrictions on the Force's movement and the monitoring of its operations.

In this regard, Pascoe welcomed President Michel Suleiman's efforts to move forward with the disarmament of militias, a key element of 1701, and stressed the need for neighboring countries and others to abide by the arms embargo imposed by the resolution.

On "the very important" Syrian-Lebanese relations, Pascoe said he was encouraged by the indications that diplomatic ties could soon be established. In addition, he lauded efforts by the Lebanese government to increase security on the border.

About a deal between Israel and Hizbullah to swap prisoners, Pascoe said: "We are very pleased with the recent movement on humanitarian aspects of 1701."

"We call on all sides to faithfully carry out those commitments," he added.

On Ban's indication in this report about his willingness to intensify efforts to find a solution to the Israeli-occupied Shebaa Farms area, Pascoe said: "The question of ownership is one for the Security Council and the parties concerned."

"What we have said is that we will certainly intensify our efforts on this but this is something that can't be imposed," he added.

Meanwhile, U.S. ambassador to the U.N. Zalmay Khalilzad reiterated the importance of the international tribunal that would try ex-Premier Rafik Hariri's suspected assassins.

He said the court would "hold accountable" those who committed the crime in Feb. 2005 and will help deter using assassinations as a way to promote a political agenda.

Khalilzad also said after the Security Council's closed-door session that there were recently positive developments in Lebanon, including the signing of the Doha accord, the election of President Michel Suleiman and the nomination of Fouad Saniora as premier designate.

But he stressed that more work needed to be done to disarm militias, demarcate the border, stop arms smuggling and find a solution to the Shebaa farms area and Ghajar.

Khalilzad said it was important to demarcate the border between Lebanon and Syria in order to solve the Shebaa issue.