Backed up by tanks and other armored vehicles, thousands of Lebanese troops moved into southern Lebanon Thursday, amid warnings by high-ranking IDF officers that Israel will resume its offensive against Hizbullah if Lebanon does not succeed in preventing it from rearming. "We will not let Hizbullah return to its original strength," one officer told The Jerusalem Post. "And if that means taking action and resuming our military offensive, then we will." The deployment of the Lebanese army - a key provision of the UN-brokered cease-fire plan that ended fighting between Israel and Hizbullah - marked a first step toward extending government control in a region Beirut has largely avoided for four decades. However, if the Lebanese army did not do the job it was tasked with, Israel would do it instead, the officer said. Armed Hizbullah guerrillas have already begun reappearing in villages along the northern border from which Israel withdrew. "We expect Lebanon to uphold its side of the agreement," the officer said. "We hope that we won't have to go back into Lebanon, but if the need arises we will not hesitate to do so." Lebanese troops took up positions in some 30 villages, including Bint Jbail, scene of some of the heaviest fighting during the war, which ended Monday morning with the cease-fire. Their deployment was based on an agreement between Israel and UNIFIL, which also plans to complete the deployment of its new international force by the end of next week. All of the IDF's reservists have left Lebanon. Infantry brigades backed up by the Armored Corps are holding a line along the security zone Israel maintained during its 18-year presence in Lebanon, which ended in 2000. Three Lebanese brigades were to deploy in southern Lebanon where they would be joined by 15,000 new UN observers. Israel, the officer said, was upholding the cease-fire even at the cost of having to restrain troops in Lebanon from striking at Hizbullah targets. "We want to give the cease-fire and the Lebanese army a chance to take control of what is going on inside southern Lebanon," he said. Meanwhile, senior IDF officers dismissed claims by Defense Minister Amir Peretz that the IDF had not accurately evaluated the threat Hizbullah posed. "The IDF was not surprised by the incessant rocket attacks, since we knew for years what Hizbullah was capable of," an officer in Northern Command said. "We knew about the threat, and we warned the diplomatic echelon about it." Beirut's international airport reopened to commercial traffic for the first time since July 13, when it was attacked by the IAF. A Middle East Airlines passenger jet touched down from Amman, ending a 36-day Israeli blockade, and a Royal Jordanian flight followed soon after. The IDF said it was coordinating the arrivals, but said it was a one-time affair and warned that it did not constitute an end to the air blockade.