By Chris Morris BBC News, Beirut

There was no sign that Mr Ban's talks achieved anything concrete

United Nations Secretary General Ban Ki-moon has heard first-hand just how hard it will be to find a compromise in Lebanon to end months of damaging political deadlock.

On his first visit to Beirut as UN chief, Mr Ban criss-crossed Lebanon's fractious political divide, talking to government and opposition leaders about the increasingly bitter stalemate which has paralysed the country's political institutions.

Among others, he met both the Western-backed Prime Minister, Fouad Siniora, and the pro-Syrian speaker of parliament, Nabih Berri - one of the key figures in the campaign to oust the government.

Speaking at a press conference with Mr Siniora, Mr Ban said dialogue and consensus were the only way forward.

There was no sign, however, that his talks achieved anything concrete. "I am of course disappointed," he said, "that the political crisis has not yet been resolved."

'Vibrant society'

Opposition protesters affiliated with Hezbollah and its allies have been camped outside the prime minister's office since early December, and much of downtown Beirut is surrounded by razor wire.

Some 12,000 UN troops are helping maintain a ceasefire with Israel

Many Lebanese are worried that a failure to reach a political compromise could lead to further sectarian tensions.

Two months ago four people were killed in street fighting in Beirut, the worst since the Lebanese civil war, and the army now maintains a highly visible presence in the city.

Mr Ban agrees that the continuing deadlock risks endangering what he called one of "the most vibrant societies in the Middle East".

But he promised that the international community remained committed to Lebanon.

He knows that the United Nations itself will be intimately involved in the country's immediate future.

On Saturday Mr Ban will visit some of the 12,000 UN troops in the south, who are helping to maintain a ceasefire after last summer's war between Israel and Hezbollah guerrillas.

Sensitive issue

During his talks in Beirut, Mr Ban welcomed the Lebanese government's commitment to UN Security Council resolution 1701, which brought the fighting to an end.

The Hariri killing sparked protests that forced Syria out of Lebanon

But he noted that some areas of compliance required more effort, notably the strengthening of Lebanese government control over its borders.

More needs to be done, in other words, to prevent the smuggling of arms from across the Syrian border to Hezbollah.

The UN has also taken a leading role in pushing for the creation of an international tribunal to try suspects in the assassination two years ago of the former Lebanese Prime Minister, Rafik Hariri.

The UN Security Council has backed the tribunal, as has the government in Beirut.

But the opposition is blocking approval in parliament - it fears that its Syrian allies will be blamed for Mr Hariri's death come what may.