A boy reacts as he mourns the loss of his sister who was killed in the aftermath of overnight Israeli bombardment in Al Maghazi, Gaza Strip, on Wednesday. AFP

As the war in Gaza nears its tenth month, Israel's top ally the United States has warned of the risk of a major conflict against Hizbollah in Lebanon, following an escalation in cross-border fire.

Israel's military said last week plans for an offensive in Lebanon were "approved and validated," prompting fresh threats from Hizbollah chief Hassan Nasrallah.

Martin Griffiths, the UN humanitarian coordinator, told reporters in Geneva that he saw Lebanon as "the flashpoint beyond all flashpoints," pointing to southern Lebanon in particular. Griffiths said he had been discussing with colleagues in Jerusalem about the prospects of what might happen there. "We are worried about the potential for further tragedy and deaths," he said. "It's potentially apocalyptic."

Griffiths, whose term finishes this week, warned that a war involving Lebanon "will draw in Syria... it will draw in others." And "it will of course have an impact on Gaza; of course it will have an impact on the West Bank. "It's very alarming," he said.

Martin Griffiths speaks during an event. File

On Tuesday, the United Nations Interim Force in Lebanon said three contractors returning home from the peacekeepers' base in the south Lebanon village of Shamaa "had their vehicle hit by gunfire," reporting "no serious injuries."

'EXCHANGES OF FIRE'

The UN's peacekeeping chief Jean-Pierre Lacroix condemned the incident, saying there was escalation on the border. "Certainly we condemn the attacks against those contractors in the same way as we condemn attacks against civilians (and) certainly attacks against our peacekeepers as well," Lacroix said at a briefing at UN headquarters in New York. "What we've seen over... the last week is, if not a full-fledged sort of escalation, but certainly an increase, a gradual increase, in the intensity of these exchanges of fire."

Since the war began, "Gaza has taught us a new level of tragedy and cruelty," Griffiths said.

"But we are all worried that it may only be the beginning." He said the UN humanitarian agency OCHA and other aid agencies were preparing for a broader crisis. "There is a lot of preparedness on the aid side," he said. But the kind of preparedness needed was "political," he stressed. "The problem is stopping this war from getting worse."

Agence France-Presse