By Jane O'Brien
BBC News, United Nations
UN investigators are expected to get an extra year for their inquiry into the murder of a former Lebanese leader.
The Hariri killing sparked protests that forced Syria out of Lebanon
Prime Minister Rafik Hariri was killed two years ago in a murder the UN says was "probably" politically motivated.
Previous UN reports have implicated Syrian and Lebanese officials.
In its latest report, the Investigating Commission said the killing may have been an attempt to derail elections which Mr Hariri was expected to win.
The head of the commission, Serge Brammertz, says his inquiry has reached a critical point and he needs more time to pursue promising new evidence.
French Ambassador Jean-Marc de La Sabliere said he expected the Security Council to agree to a year's extension.
Mr Brammertz's team is examining calls made via six mobile phones used by the bombers and which they hope could lead directly to those responsible for the attack.
Mr Brammertz says it is essential to prosecute suspects
Mr Brammertz said his commission has identified "further information of interest... including possible surveillance and reconnaissance activity, possible practice-runs or earlier attempts to kill Rafik Hariri".
The identity of one of the bombers who was killed in the blast is still unknown, but DNA tests on 33 body parts have suggested that he was not a native of Lebanon.
The team may be able to trace his home country from the high levels of lead he was exposed to as a child.
Geographical samples have been taken from a number of Middle East regions including Syria.
The commission has also widened its inquiry to include attacks on its own team, the murder of Lebanese minister Pierre Gemayel in 2006 and the Ain Alaq bus bombings near Beirut last month.
But the issue of how to prosecute anybody implicated by the investigation remains contentious - even though Mr Brammertz says it is essential.
"It's absolutely the next logical step after the investigation to commission a tribunal," he told the BBC.
"Without this step it would be complicated or difficult to justify even the existence of this [investigative] commission."
The UN has signed an accord that would create an international tribunal but the move has been opposed by Syria and Lebanese President Emile Lahoud.
The Syrian president, Bashar al-Assad, has said any Syrian suspects would be tried in Syria and he would not release them to a tribunal.
And if Lebanon fails to ratify the proposal, the Security Council may consider independently authorising a tribunal as it did in Rwanda and the former Yugoslavia.
"But the general feeling is that it's better to let the Lebanese parties themselves reach a solution rather than push it too hard from New York," said Colin Keating, executive director of the Security Council Report think-tank and former New Zealand UN ambassador.
"Also, it was always known that extradition issues would have to be resolved. Simply establishing a tribunal doesn't cross that bridge - but we still have many months to go before it's an issue," he said.
A summit of the Arab League is due to be held in the Saudi Arabian capital of Riyadh next week in the hope of building a consensus that will allow the tribunal to go ahead.
Mr Keating said people would be waiting to see the outcome of that before considering any further action.