Syria's embattled leadership faced further diplomatic pressure yesterday after a United Nations special envoy accused it of defying the world body by failing to end all military and security activity in Lebanon.

While Damascus claimed to have severed all military links with its small neighbour, a UN assessment, leaked to the Israeli newspaper Haaretz, said that Syrian influence had simply been driven underground. The assessment, by Terje Roed-Larsen, said that Syria continued to smuggle weapons to various militias in Lebanon that were willing to do its bidding.

Lebanese security still struggle against Syrian-backed militia Intelligence work also continued, with Syrian proxies in Lebanon taking orders from Damascus.

That was a clear breach of Security Council resolution 1559, which demanded Syria's full withdrawal of its military and security personnel from Lebanon and an end to its meddling. The report is expected to add to the pressure on Syria following last week's publication of another UN report into the murder of Rafik Hariri, the former Lebanese prime minister, in Beirut on Feb 14.

The Security Council will meet in public tomorrow to consider the findings of the Hariri report. It said there was "converging evidence" of Syrian involvement, although further investigation was needed before any individuals, Syrian or otherwise, could be charged.

Britain has called for economic sanctions to be considered against Syria. But the council is likely to give Damascus two more months fully to comply with the Hariri investigation.

Condoleezza Rice, the US secretary of state, appearing at a press conference with Jack Straw, the Foreign Secretary, said that doing nothing was not an option for the UN.

Infuriated by Syrian involvement in the Iraq rebellion, Washington and London are now gleeful over the trials of President Bashar al-Assad.

"Bashar made his bed; now he has to get out of it by himself," a senior US source said. A British source said: "Syria being on the back foot is no bad thing." If the situation is handled well, Syria could be made to stop supporting the Iraq rebellion, deny support to Palestinian militants and isolate Lebanese extremists such as Hizbollah.

If it goes badly - if for example the regime collapses and Syria is swept by violent Islamists - the fires in Iraq, Palestine, Lebanon and Syria could merge into a single conflagration. For the moment America seems to be listening to the French, British and Arab view, shared even by Israel, that stability is better than chaos, that a weakened President Assad is better than no Assad.

The Lebanese responded to the Hariri report by arresting Mahmoud Abdel-Al, who was said to have telephoned their president, Emile Lahoud, shortly before Mr Hariri was blown up.

There were unconfirmed reports of 11 more arrests in Lebanon arising out of the report.