Hezbollah fired more than 200 rockets into Israel today, the heaviest missile barrage mustered by the militant group in more than three weeks of fighting.

As of early this evening, Israeli authorities had reported the landing of 210 rockets, including at least one longer-range Khaibar-1 missile, which landed 60km (37 miles) south of the Lebanese border, the furthest a rocket has flown into the country.

One American-born Israeli was reported to have been killed in the attacks. The man, who has not been named, was hit as he rode a bicycle in Kibbutz Saar, a communal farm near the coastal resort of Nahariya, local officials said. A further 21 people were wounded in the strikes.

Fifty-five Israelis, including 19 civilians, have now died in the conflict against Hezbollah, which began three weeks ago when eight Israeli soldiers and two were kidnapped during a raid by the militant group on the Lebanese-Israeli border. More than 750 Lebanese civilians and hundreds of Hezbollah fighters are believed to have lost their lives.

Fighting in southern Lebanon continued throughout the day with reports that Israeli ground troops were attacking Hezbollah positions in five districts with the support of airstrikes and artillery. More than 6,000 Israeli soldiers have been sent across the border to sweep out Hezbollah guerrillas from well-defended strongholds.

Hezbollah fighters defended their bases with machine guns, mortars and anti-tank fire today in several battles near the village of Aita Shaab, where there was intense Israeli shelling and air strikes, a source in the UN peacekeeping force told Reuters. Israeli forces were reported in five areas of the south after soldiers were dropped from helicopters near the border village of Meis al-Jabal.

Lebanese military sources said the Israelis had captured a hilltop at al-Aweida overlooking several villages, including Kfar Kila and Adaiseh.

No casualties were reported among the Israeli soldiers. Hezbollah claimed to have destroyed four tanks and an armoured bulldozer and to have "repulsed the attackers". Yesterday, three Israeli soldiers were killed and 25 were wounded in bitter fighting around Aita Shaab.

Today's clashes came after last night's helicopter-led raid on the town of Baalbek, 95km (60 miles) inside Lebanon, where Israeli commandos attempted to capture Hezbollah leaders.

Ten Hezbollah fighters were killed in a four-hour gun battle around an evacuated hospital. Eventually, five suspects were flown back to Jerusalem, according to the Israeli army. But Hezbollah denied that the men taken were members of the group.

The night raid was backed by air strikes in which 19 civilians died, including four children. One family was wiped out when a missile hit their garden, while a Bedouin women and five of her children were gunned down by Israeli soldiers when they were frightened by an Israeli helicopter landing nearby and ran out of their tent, neighbours claimed.

This morning, the chief of the Israeli army that the operation showed Israel could strike at will inside Lebanon.

"We can and will operate anywhere in Lebanon to achieve our ends," said Dan Halutz, the Israeli Defence Force chief of staff, who told reporters that Israeli troops had now killed more than 300 Hezbollah fighters and substantially weakened the group's missile capabilities.

Ehud Olmert, the Israeli Prime Minister, later claimed that Hezbollah's infrastructure was "entirely destroyed". That was before the beginning of this afternoon's record-breaking barrage. Until today, the most rockets fired by Hezbollah in a day was Sunday, when 157 strikes were reported.

Across the border, Lebanese officials said the damage caused by three weeks of Israeli airstrikes would cost more than $2 billion to repair. Mohammed al-Safadi, the Lebanese Transport and Public Works Minister, said that roads, bridges and flyovers have been destroyed across southern and eastern Lebanon. Beirut airport is expected to take three months to repair.

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