Four Israeli soldiers, guns slung over their shoulders, pulled up in a truck and welded together a broken, rusting flag pole on their side of the border before driving off, perhaps to return later with a blue-and-white Israeli flag to set up a permanent post. 

Two Hezbollah guerrillas milled around at a nearby observation post. U.N. peacekeepers positioned between the enemies watched. 

Wednesday was an uneventful day in southern Lebanon, although it came between two Palestinian suicide bombings in Jerusalem that killed a total of 26 Israelis and prompted Israeli military retaliation, further sharpening tension in the Middle East. 

Observers and foreign diplomats say that although the Lebanon-Israeli front is calm now, the potential for trouble can't be ignored. Escalating Israeli-Palestinian violence, desire on the part of Lebanese guerrillas and Palestinian refugees in Lebanon to help the Palestinians, neighboring Syria's efforts to influence any Mideast settlement and even dangerous rhetoric could lead to fighting. 

The New York Times last weekend quoted a senior Western diplomat in Washington as warning of the increased threat of military action on the Lebanese-Israeli border in which Hezbollah rockets launched deep into Israel could prompt severe retaliation, including a ground invasion. 

U.S. administration officials have discounted an immediate or new threat while acknowledging that the situation remained volatile. 

Thursday, Hezbollah guns opened up on a high-flying jet with seven shells from a 57-mm gun near the border, Lebanese security officials said. Israeli warplanes have been flying reconnaissance missions over Lebanon, occasionally breaking the sound barrier and drawing anti-aircraft fire from Hezbollah guerrillas. Fragments of Hezbollah shells have crashed in Israeli territory, causing panic among border residents. 

Such skirmishing has been accompanied by verbal saber-rattling. 

"The time when we used to get hit, bombed and killed and we didn't hit back is over ... They [Israelis] should know that we will strike back twofold," Hezbollah leader Sheik Hassan Nasrallah said Tuesday at an anti-Israel conference in Beirut that featured representatives of the Lebanese government and Palestinian militants — including Hamas, the group that claimed responsibility for a suicide bus bombing in Israel on Tuesday. 

Israel's military chief of staff, Lt.-Gen. Shaul Mofaz, told an Israeli parliamentary committee on Wednesday that the threat from Hezbollah is increasing and that Israel had informed the United States that Syria would be the target of any Israeli response to a Hezbollah attack. Syria is the main power broker in Lebanon and one of Hezbollah's sponsors. 

Some analysts fear an Israeli attack on Syria could spark a wider Arab-Israeli war. Lebanon's government, concerned about what it sees as Israeli threats, summoned foreign ambassadors on Thursday and U.S. Ambassador Vincent Battle afterward called for calm in the border area. 

According to Timur Goksel, senior adviser to the commander of U.N. peacekeeping forces, U.N. forces have observed no military changes, nor any rockets being set up to attack Israel in the area of U.N. deployment along parts of the border. Israeli government and media have reported Hezbollah had thousands of rockets, some long-range, that could be launched deep into Israel. 

"I am not aware of a single person in south Lebanon who has seen such rockets," Goksel told The Associated Press at his headquarters in the border town of Naqoura on the Mediterranean. "I am not saying they don't have them but if they had them they've done a good job at concealing them." 

Hezbollah in the past has hidden rockets in the bush and in valleys and buried caches. The guerrillas who place and set off rockets don't use roads to travel and are careful not to be spotted. 

In April, at the height of an Israeli invasion of the West Bank, Palestinian guerrillas shot rockets and bullets into Israel from Lebanon and Hezbollah guerrillas repeatedly lobbed rockets on Israeli positions in the disputed Chebaa Farms area, prompting Israeli airstrikes. 

U.S. Secretary of State Colin Powell, who met Lebanese and Syrian officials in April, is credited with extinguishing that flare-up.