The move has further complicated the struggle by world powers to agree on the makeup and role of an international force to police the fragile ceasefire.
"They will close the frontier for all traffic (if) the UN troops will be deployed along the border”, Finnish Foreign Minister Erkki Tuomioja told reporters following talks in Helsinki with Syrian counterpart Walid Muallem.
Syrian President Bashar al-Assad also warned that deploying foreign troops along the border as envisioned under the UN resolution would be considered a "hostile" act against his country.
Israeli public radio reported that Israeli Prime Minister Ehud Olmert has conditioned the lifting of an air and sea blockade of Lebanon on the deployment of international troops at Beirut airport and on the Syrian border.
Resolution 1701 calls on Lebanon to secure its borders and other entry points to prevent illegal arms coming into the country.
Washington and Israel accuse Syria of acting as a transit point for shipments of arms and other supplies from Iran to Hezbollah.
Iran and Syria deny the claim.
Reacting to the comments Lebanese Prime Minister Fuad Siniora said Lebanon would act to preserve its sovereignty and independence.
Lebanon and Syria must have mutual respect for each other, he said, because "we have no interest in being in disagreement with Syria while Syria has no interest in being in disagreement with us."
Asked whether the United States took Damascus's reservations about the troop deployment seriously, White House spokeswoman Dana Perino simply replied: "No".
Meanwhile, Lebanese troops were deploying along the Syrian border in the north and east of the country, military sources said.
"Several brigades have deployed at all the crossing points on the Mediterranean coast in the north, and as far as the Rashaya region," in the southeast, a source told AFP.
The warning came as EU diplomats met in Brussels to prepare for a meeting of foreign ministers on Friday.
The meeting, which will be attended by UN Secretary General Kofi Annan, will try to hammer out which countries will come on board a peacekeeping force.
Pressure is growing on EU members to overcome indecision on how many troops they are willing to provide and under what conditions, especially after France offered far fewer than originally expected.
EU foreign policy chief, Javier Solana has spoken from the start about 4,000 European soldiers, far fewer than the force of 15,000 troops envisaged in the resolution.
In addition to being ready to lead the force, Italian Prime Minister Romano Prodi has offered some 3,000 troops, although he insisted a new Security Council resolution was needed to clearly define the peacekeepers' role.
France has come under criticism for sending just 200 soldiers to the expanded force.
They had been expected to send between 2,000 and 3,000 troops.
Kofi Annan will travel on from Brussels to the Middle East in his bid to speed up implementation of Resolution 1701.