Eight armoured personnel carriers had moved into position close to the offices, located near the Hotel Beau Rivage and the seafront in southern Beirut, and a number of troops were seen on foot.
A Lebanese officer at the scene said the move was a "prelude to the Lebanese army taking charge of positions that will be evacuated by the Syrian army."
Syrian troops remained in their quarters, where sentinels were posted outside.
It came just hours before a keynote address by Syrian President Bashar al-Asad to the Syrian parliament amid mounting international calls for a complete withdrawal of Syria's 14,000 troops from Lebanon.
There was no confirmation whether al-Asad would be announcing a redeployment within Lebanon itself or would go some way towards ceding to the international pressure for a full pullout.
The bulk of Syrian troops that had been stationed in and around Beirut have been withdrawn in five successive redeployments since 2002, and the only remaining forces are at the intelligence headquarters.