Beirut, Lebanon ? Israeli troops sealed off a Hezbollah stronghold Tuesday and widened their foothold in southern Lebanon, but officials said Israeli bombs killed six people in a south Lebanon town and three U.N. observers in a border outpost with another feared dead.

Secretary of State Condoleezza Rice and other key Mideast players gathered in Rome for a meeting today to discuss proposals for ending the fighting that has claimed more than 400 lives. Key issues were how to disarm Hezbollah and assemble an international peacekeeping force to enforce the peace along the Israel-Lebanon frontier.

U.N. Secretary-General Kofi Annan said the strike on a clearly marked U.N. border outpost was “apparently deliberate” and demanded Israel investigate. A bomb dropped by an Israel warplane scored a direct hit on the post in the town of Khiyam, near the eastern sector of the border, U.N. officials said.

Annan said two observers were killed with two more feared dead. Later, a U.N. official confirmed that a third body had been recovered. The official spoke on condition of anonymity because he was not authorized to publicly discuss the issue.

One of the dead was identified as Chinese U.N. observer Du Zhaoyu, China’s official Xinhua News Agency reported. The other three were from Austria, Canada and Finland but it wasn’t clear which two were confirmed killed, U.N. and Lebanese military officials said.

Israel’s U.N. Ambassador Dan Gillerman expressed his “deep regret” for the deaths and denied Israel hit the post intentionally.

Israeli commanders said they would not push deep into Lebanon but were determined to stop Hezbollah missiles that have continued despite Israel’s punishing raids on Hezbollah targets. A new volley of Hezbollah rockets hit northern Israel, killing a teenage girl, and Hezbollah’s leader, Sheik Hassan Nasrallah, issued a taped television message saying guerrillas would now start firing rockets deeper into Israel.

Tuesday marked a month since the start of what is now a two-front war between Israel and Islamic militants. On June 25, an Israeli soldier was captured by Hamas militants in Gaza, prompting an Israeli offensive there. Two weeks into that flare-up, Hezbollah snatched the two other soldiers.

Israel and the United States say their ultimate aim is to fundamentally reshape Lebanon to end Hezbollah’s presence by the border, strengthen democracy in the country and ensure lasting peace with Israel. In the process, Lebanon has been ravaged, with hundreds killed, nearly a half-million driven from their homes and vast damage to roads and bridges.

Israel is facing tougher than expected resistance as it makes it first small ground steps into hilltop villages across the border. Its troops sealed the town of Bint Jbail and battled for a second day Tuesday against around 200 guerrillas inside.

Troops also moved on the nearby village of Yaroun, fighting guerrillas there. Fifteen Americans fled Yaroun in a convoy of 80 cars carrying residents that reached the southern port of Tyre on Tuesday.

Hezbollah reported two guerrillas killed in the day’s fighting, while Israel said three of its soldiers were wounded. The Israeli military said Hezbollah’s commander for the central border sector, known as Abu Jafr, was killed.