The envoy, Terje Roed-Larsen, said Lebanon's inability to exert control over some areas or rein in the militias was stalling its progress toward achieving full sovereignty after years under Syrian dominance.
"Tangible results are yet to be achieved in these two fields, and I will continue my efforts in this regard," wrote Terje Roed-Larsen on Wednesday.
While that step has been encouraging, the requirement to disarm, a clear reference to the Syrian- and Iranian-backed group Hizb Allah, has not been met, Roed-Larsen said.
So too has there been little significant change in Lebanon getting control over all its territory.
Roed-Larsen is UN Secretary-General Kofi Annan's special envoy for implementation of Security Council resolution 1559, which called for Syria to withdraw all military forces and intelligence operatives as well as the disarmament of all militias in Lebanon.
"Tangible results are yet to be achieved in these two fields, and I will continue my efforts in this regard"
The report comes as the UN Security Council tries to pressure Syria to cooperate better with a UN-backed investigation into the 14 February assassination of Lebanon's former prime minister, Rafiq al-Hariri.
Roed-Larsen's observations could be another tool in that effort.
Syria withdrew its troops and intelligence officials last April, ending the country's 29-year presence in its smaller neighbour which began when Damascus sent troops to help quell what was then a year-old civil war.
While resolution 1559 was adopted a year ago, it was al-Hariri's assassination, and the massive anti-Syrian protests it sparked, that spurred the Syrians to leave.