Kofi Annan, the UN secretary-general, said that he was "deeply concerned" by the violation of the ceasefire.
A spokesman for Annan said in a statement: "The secretary-general is deeply concerned about a violation by the Israeli side of the cessation of hostilities as laid out in Security Council resolution 1701."
The statement from the UN comes after the Lebanese threatened to halt the deployment of troops to the south of Lebanon if the violation was not recognised.
Elias Murr, the Lebanese defence minister, said after a meeting with UN representatives on Saturday: "If there are no clear answers forthcoming on this issue, I might be forced to recommend to the cabinet early next week the halt of the army deployment in the south."
Meanwhile, the first small contingent of reinforcements for the peacekeeping force - 49 French soldiers - landed on Saturday at the southern Lebanese coastal town of Naqura, with 200 more expected next week.
However, Mark Malloch Brown, the UN deputy secretary-general, said more countries need to step forward to fill out a vanguard of 3,500 troops that the UN wants on the ground by August 28 to help ensure that the truce between Israel and Lebanon holds.
Murr said the Israeli raid could spark Hezbollah retaliation, which in turn could lead to Israeli reprisals. He suggested that Israel might be trying to provoke a response so that it could have an excuse to attack the Lebanese army.
The Israeli raid took place deep
inside Lebanese territory
He said: "We will not send the army to be prey in an Israeli trap."
Under the ceasefire terms, Israel has said it will conduct defensive operations if its troops are threatened.
But the raid took place far from the positions of Israeli troops in southern Lebanon.
The ceasefire resolution talks about an end to weapons shipments to Hezbollah as part of a long-term end to the conflict - but does not require it under the immediate truce.
According to Israel, the raid that was carried out in the early hours of Saturday morning was defensive and designed to disrupt weapons supplies from Syria and Iran to Hezbollah.The Israeli military said such operations would continue until "an effective monitoring unit" was in place to prevent Hezbollah from rebuilding its arsenal.
Mark Regev, the Israeli foreign ministry spokesman, said
: "If the Syrians and Iran continue to arm Hezbollah in violation of the [UN ceasefire] resolution, Israel is entitled to act to defend the principle of the arms embargo.
Hezbollah fighters inspect the
site of the Israeli raid
"Once the Lebanese army and the international forces are active ... then such Israeli activity will become superfluous."
Another Israeli minister said Israel will continue to carry out raids in Lebanon aimed at halting alleged weapons smuggling to Hezbollah from Syria.
"As long as the Lebanese army and the international forces are not deployed (in south Lebanon), the Israeli army will not stop its flights in the region to stop the transfers of arms from Syria," Gideon Ezra, the environment minister who is considered close to Prime Minister Ehud Olmert, told public radio.
Saturday's operation, risking the ceasefire, suggested Israel was going after a major target near Baalbek - perhaps to rescue two Israeli soldiers snatched by Hezbollah on July 12, or to try to capture a senior Hezbollah official to trade for the soldiers.
An Israeli soldier was killed in the operation.