A security source said the Syrians had not vacated two major intelligence offices and two military positions in and around the town of Tripoli on Friday but could do so within 24 hours.
All other military positions, including a large base at an airstrip, were evacuated overnight and thousands of soldiers and hundreds of vehicles crossed into Syria, witnesses said.
Syrian forces first entered Lebanon in 1976 early in the civil war. Their numbers have declined to 14,000 from a peak of 40,000, but they have never before left positions in the north.
Syrian troops also continued to return home or move eastwards from the Beirut area in line with a phased withdrawal plan agreed this week amid intense global pressure on Damascus to lift its military and political grip on Lebanon.
Lebanon's pro-Syrian cabinet fell last week after an outcry over the assassination of former Prime Minister Rafiq al-Hariri, but Umar Karami, the man who headed it, was asked on Thursday to form what he said would be a national unity government.
Anti-Syrian opposition leaders reacted coolly to that idea and said Karami's reappointment would only prolong political uncertainty ahead of parliamentary elections due by May.
"We don't think this appointment gives the Lebanese hope"
Walid Jumblatt, Druze leader
"We don't think this appointment gives the Lebanese hope," Druze leader Walid Jumblatt was quoted in the local press as saying during a visit to Moscow. He described the move as "a disappointment and an extension to the crisis".
A group of Christian MPs said: "Reinstating premier Umar Karami to form a new government after the opposition made its demands shows Syria's insistence on maintaining its tutelage policy that was rejected by the Lebanese."
Opposition leaders have said they wanted a cabinet excluding election candidates. They are also demanding a full Syrian pullout, the sacking of pro-Syrian security chiefs and an international inquiry into last month's assassination of al-Hariri.
Karami will start consulting political and religious leaders, including some in the opposition, on Monday, political sources said. Pro-Syrian ministers dominated his last cabinet.
The United States, which has been demanding that Syria end its involvement in Lebanon, criticised Karami's reappointment.
"Prime Minister Karami said when he resigned the first time that he was resigning because he couldn't be effective," State Department spokesman Adam Ereli said. "If ever there were a time that Lebanon needed effective government, that time is now."
UN envoy Terje Roed-Larsen, expected to press for a timetable for a complete Syrian withdrawal in line with a UN Security Council resolution, will travel to Damascus on Saturday for talks with Syrian President Bashar al-Asad.
About 7000 Syrian troops were
moved under the pullout plan
He is to meet Lebanese officials in Beirut on Sunday.
Defence Minister Abd al-Rahim Murad said on Thursday that about 7000 Syrian troops were on the move under the pullout plan agreed by Lebanese President Emile Lahud and al-Asad on Monday.
"Most of those withdrawing are going to Syrian territory," Murad said.
He said the first phase of the plan, which calls for Syrian forces to move from the north and the Beirut area to the Bekaa Valley, would be completed in about a week's time.
Beirut and Damascus will then decide how long any Syrian troops remain.