A spokesman of the Israeli medical service Megen David Adom told Xinhua on Friday that 20 people were wounded during the past half hour by rockets fired by Lebanon's Hizbollah militia onto northern Israel.

The spokesman said that one of the wounded was in critical condition, four sustained moderate injuries and others were slightly wounded.

Meanwhile, an Israeli army spokeswoman told Xinhua that during the past half hour, around 30 Katyusha rockets fired by Hizbollah militia hit several Israeli communities along the northern border with Lebanon.

Earlier in the day, the army said that more than 150 Katyusha rockets had been fired onto about 20 neighborhoods along Israel's northern border area, killing two persons and wounding 90 others.

On Thursday, Katyusha rockets struck Haifa, Israel's third largest city, for the first time since violence between Israel and Hizbollah broke out on Wednesday. No casualties were caused.

Some 220,000 Israelis stayed in bomb shelters in northern Israel on Thursday night to avoid the rocket fire, the Israeli army said.

Following the Haifa attack, Israeli Defense Minister Amir Peretz said that Hizbollah had broken rules, vowing to make the militia "pay a heavy price."

Peretz, who spoke to reporters after a special security meeting in Tel Aviv, said that Israel would "strike with resolve the organization that broke the rules and wants to lead the entire Middle East into a tailspin."

According to local newspaper Ha'aretz, Hizbollah warned on Friday that it might launch an attack on Haifa at any time.

Tensions between Israel and Lebanon have been drastically heightened since Wednesday when Lebanon's Hizbollah militia kidnapped two Israeli soldiers and killed eight during border clashes with Israeli troops.

In response, Israel waged intense air raids on Lebanon's targets and blockaded Lebanese sea ports.

The Israeli army said that Israeli forces carried out several operations on Friday morning against a total of 18 Lebanese targets, including the headquarters of Hizbollah in Beirut and a number of Hizbollah outposts in southern Lebanon.

On another front, Palestinian militants fired eight rockets from the Gaza Strip onto the southern Israeli city of Sderot on Friday. Four Israelis were treated for shock and a building was damaged and set ablaze.

Israeli forces continued a three-week-old massive ground and air offensive in the Gaza Strip on Friday in a bid to rescue an Israeli soldier kidnapped by Gazan gunmen and halt Palestinian rocket attacks.