Beirut, Lebanon ? Israeli troops punched into south Lebanon on Wednesday as warplanes flattened houses and buildings including one thought to hold Hezbollah’s top leaders, intensifying an offensive despite mounting international pressure and a Lebanese appeal to spare the country further death and devastation.

The attempt to wipe out the Hezbollah leadership was the most dramatic action on a day that saw the Israelis clash with the guerrillas and the Lebanese prime minister say about 300 people in his country had died in the eight-day offensive.

Reports of the death toll in Wednesday’s violence ranged as high at 70, which would make it the single deadliest day since the fighting began. Voice of Lebanon state radio reported 70 dead, while other Lebanese media gave figures ranging from 57 to 64. No further breakdowns were provided.

U.N. High Commissioner for Human Rights Louise Arbour criticized the growing death toll, saying the indiscriminate shelling of cities and of nearby military sites was invariably resulting in the deaths of innocent civilians.

“International law demands accountability,” Arbour said in Geneva. “The scale of the killings in the region, and their predictability, could engage the personal criminal responsibility of those involved, particularly those in a position of command and control.”

Israel broadcast warnings into south Lebanon telling civilians to leave the region, a possible prelude to a larger Israeli ground operation.

Hezbollah, undeterred, fired rockets into the Israeli Arab town of Nazareth, where Jesus is said to have spent his boyhood, killing two Arab brothers, ages 3 and 9, as they played outdoors.

Hezbollah denied that any of its “leaders or members” died in the strike in the Bourj al-Barajneh district of south Beirut. The explosives did not blast a leadership bunker, but a mosque under construction, the group said in a statement that was faxed to The Associated Press.

In a statement, the Israeli military spokesman’s office said: “We attacked a bunker of Hezbollah leaders in the Bourj al-Barajneh neighborhood of Beirut.” The military said the attack took place between 8 p.m. and 9 p.m. and involved 23 tons of explosives.

Last Friday, Israel bombed leader Sheik Hassan Nasrallah’s headquarters but both he and his family survived.

Prime Minister Fuad Saniora, whose weak government has been unable to fulfill a U.N. directive to disarm Hezbollah and put its army along the border with Israel, issued an urgent appeal for a cease-fire. He said his country “has been torn to shreds,” and pointedly criticized the U.S. position that Israel acts in self-defense.

“Is this what the international community calls self-defense?” a stern-looking Saniora asked a meeting of foreign diplomats including U.S. Ambassador Jeffrey Feltman. “Is this the price we pay for aspiring to build our democratic institutions?”

Israel vowed to press the offensive in Lebanon until it destroys the militant Shiite guerrillas’ vast arsenal of missiles and drives Hezbollah fighters far from its northern border.