On May 20, at the outbreak of the clashes in Lebanon, Syria shut two other border posts, at Arida and Dabussiya.
Two other crossings remain open, notably on the main Damascus-Beirut highway.
The Lebanese government and the UN also say other groups, including the Palestinian Front for the Liberation of Palestine - General Command, are rearming.
Marwan Hamada, the Lebanese telecommunications minister, told Al Jazeera: "We have provided the UN Security Council with a full set of proofs on the interruption of weapons on the reinforcement of positions of Palestinians related to Syria."
The armed Palestinian presence in Lebanon has come under renewed scrutiny following the crisis at Nahr al-Bared.
Almost three years ago, the UN adopted resolution 1559 which calls for the disarmament of all Lebanese and non-Lebanese groups – a reference to Palestinian factions.
But government officials say they have no intention of opening new fronts against any armed group at least for the time being.
And the PFLP-GC and other groups allied with Syria, such as Fatah Intifada, insist the weapons will not be used against Lebanon, but they have no intention of dismantling their bases.
Abu Adnan Odeh, a PFLP-GC official, said: "When Palestinians live in stability, we will discuss our weapons. This issue should be solved politically.
"We have been targeted by some groups in the Lebanese government because they are implementing the American plan in the region."
Palestinian camps are off limits to the Lebanese state under an Arab agreement reached decades ago.
All factions are armed and regulating weapons inside the various camps is a government demand as well.
But as yet, there has been no consensus among Palestinian groups on how this can be done.