JERUSALEM -- Hamas militants in the Gaza Strip fired dozens of rockets and mortar shells into southern Israel on Wednesday in the heaviest bombardment on the area in months, drawing ominous Israeli threats of retaliation and dangers of escalation.

The violence came a day after a landmark visit to Gaza by the emir of Qatar. Israeli officials suggested the visit, the first by a head of state to the Hamas-ruled territory, emboldened the militant group.

The rocket fire began shortly after the emir left Gaza late Tuesday and continued through the night. Israeli officials said more than 80 projectiles were fired, and Hamas claimed responsibility for many of the attacks.

Israel responded with a series of airstrikes on rocket launchers, killing two Palestinian militants, according to Gaza medical officials.

Three Thai labourers working on an Israeli farm were wounded, two seriously, when a rocket hit a chicken coop. Other rockets badly damaged five houses and broke car windows. Schools in the area were closed.

Many people spent the day indoors, while others stayed in close proximity to the makeshift cement shelters found in the streets of southern Israeli towns. In one farming community, shrapnel covered trees and a children's playhouse in a backyard.

"Sometimes it feels like a scene out of the movie 'Platoon,' something out of the Vietnam war. We can stay at home and just hear the noise of the war," said Tamara Cohen, a resident of the border community of Ein Habesor whose children, ages 9 and 5, spent the night in a fortified "safe room" in their home.

A video issued by Hamas' military wing showed six rockets peeling off in rapid succession, then later, from what appears to be a different location, eight rockets shoot off, leaving plumes of black smoke behind them. Hamas said the video was made earlier in the day, though it provided no proof.

Hamas officials shuttered schools in border areas. Residents said they worried an escalation of fighting would ruin the upcoming Muslim celebration of Eid al-Adha, when Gaza residents feast, visit families, dress their children in new clothes and take them out to play.

Despite the violence, streets in Gaza City were crowded with residents snapping up clothes and food ahead of Friday's start of the holiday. Traffic jams blocked main roads, and prayer leaders chanted songs for the feast.

Israeli leaders threatened tougher action against the rocket fire.

"We didn't ask for this escalation and didn't initiate it," Prime Minister Benjamin Netanyahu said after touring a missile defence battery. "But if it continues, we are prepared to embark on a far more extensive and penetrating operation." The army said the "Iron Dome" defence system intercepted at least eight rockets.

Defence Minister Ehud Barak told Israel Radio that "if we need a ground operation, there will be a ground operation. We will do whatever necessary to stop this wave" of violence.

Israel carried out a broad military offensive in Gaza nearly four years ago in response to years of rocket fire. Salvos from Gaza have largely subsided since then, though sporadic violence persists.

The territory is home to numerous militant groups, including murky al-Qaida-inspired organizations that do not answer to Hamas. Gaza has also been flooded with weapons in recent years, many of them believed to have been smuggled from northern Africa and into Gaza through tunnels under the Egyptian border.

On Wednesday, the African country of Sudan accused Israel of carrying out airstrikes that blew up a weapons factory in the capital, Khartoum. Israeli officials did not comment, but analysts said that if the reports were true, the airstrike might have attacked a weapons smuggling route. Sudan has accused Israel of being behind a similar attack on an arms convoy in 2009.

Hostilities in Gaza have been simmering for weeks, with militants sporadically firing rockets into Israel and the Israeli air force responding with airstrikes.

Hamas, which has killed hundreds of Israelis in suicide bombings and other attacks, has largely avoided attacks since a devastating Israeli military offensive nearly four years ago. Instead, smaller groups have been behind most rocket fire, sometimes with Hamas' tacit blessing and sometimes against its wishes.

While Hamas remains virulently anti-Israel, it has sought to keep things quiet as it consolidates its control of Gaza. The group violently seized the territory from the rival, Western-backed Fatah movement five years ago.

Tuesday's visit by Qatar's emir, Sheik Hamad bin Khalifa Al Thani, gave a powerful boost of legitimacy to Hamas rule, which is not internationally recognized.

Hamas officials said the emir urged Hamas to do everything possible to avoid violence with Israel. Israel's foreign minister, Avigdor Lieberman, suggested the visit had the opposite effect.

"I think what we see, especially yesterday, the visit of the emir of Qatar in Gaza, it's clear support for terror and terrorist activity," he said at a news conference with the visiting EU foreign policy chief, Catherine Ashton.

In his meeting with Ashton, Israeli President Shimon Peres charged that Qatari money is funding Hamas attacks. "No one in the world could agree to the current situation" of repeated rocket salvos, Peres said.

Hamas spokesman Fawzi Barhoum accused Israel of trying to raise tensions. He said Israel was upset about the "political and economic gains" reaped from the emir's visit, and wanted to "disrupt the atmosphere ahead of the holiday."

Mukheimar Abu Sada, an independent analyst in Gaza, said Hamas had no interest in clashing with Israel now but likely felt pressured after two of its men were killed in an Israeli strike late Tuesday.

"Hamas is under pressure from the people: 'Where is the resistance that you speak of?' Hamas needed to save face," Abu Sada said.