Lebanon expelled around 70 Syrian officers and soldiers on Saturday, returning them to Syria after they crossed into the country illegally via informal routes, a Lebanese security official and a war monitor said.

Many senior Syrian officials and people close to the former ruling family of Bashar al-Assad fled the country to neighbouring Lebanon after Assad's regime was toppled on Dec 8.

The Syrian Observatory for Human Rights (SOHR), a London-based organization with sources in Syria, and the Lebanese security official said Syrian military personnel of various ranks had been sent back via Lebanon's northern Arida crossing.

SOHR and the security official said the returnees were detained by Syria's new ruling authorities after crossing the border.

The new administration has been undertaking a major security crackdown in recent days on what they say are "remnants" of the Assad regime. Several of the cities and towns concerned, including in Homs and Tartous provinces, are near the porous border with Lebanon.

The Lebanese security official said the Syrian officers and soldiers were found in a truck in the northern coastal city of Jbeil after an inspection by local officials.

Lebanese and Syrian government officials did not immediately respond to written requests for comment on the incident.

Reuters reported that they included Rifaat al-Assad, an uncle of Assad charged in Switzerland with war crimes over the bloody suppression of a revolt in 1982.

Two Lebanese security officials had said Rifaat had flown out of Beirut to Dublin recently with "many members" of the Assad family.

Earlier this month, Lebanese Interior Minister Bassam Mawlawi said top Assad advisor Bouthaina Shaaban had flown out of Beirut after entering Lebanon legally. In an interview with Al Arabiya, Mawlawi said other Syrian officials had entered Lebanon illegally and were being pursued.