The Israeli army on Wednesday intensified its offensive on the Hamas-run Gaza Strip, striking Hamas sites and killing at least 14 people on the second day of a military operation it says is aimed at quelling rocket fire against Israel.

The offensive has set off the heaviest fighting between Israel and the Islamic militant group Hamas since an eight-day battle in November 2012. Militants have unleashed rocket salvos deeper into Israeli territory than before, and Israel mobilized thousands of forces along the Gaza border for a possible ground invasion into the Palestinian territory.

Israel's defense minister warned the offensive would be long-term.

"The operation against Hamas will expand in the coming days, and the price the organization will pay will be very high," Defense Minister Moshe Yaalon said.

Since the offensive began Tuesday, Israel has attacked more than 400 sites in Gaza, killing at least 41 people. The strikes came after militants fired more than 160 rockets at Israel, including one that reached the northern Israeli city of Hadera for the first time. The city is about 100 kilometers (60 miles) from Gaza.

The army said it attacked more than 160 sites in Gaza early Wednesday, including 118 concealed rockets launching sites, six Hamas compounds — including naval police and national security compounds — 10 militant command centers, weapons storage facilities and 10 tunnels used for militant activity and to ferry supplies in from Egypt. The border between Gaza and Egypt has effectively been closed for months.

Gaza health official Ashraf Al-Kedra said Wednesday's airstrikes killed one militant in south Gaza, an 80-year-old woman, the son, wife and neighbor of a Hamas militant, and three others whose affiliation was not immediately known.

Israel's army said it targeted a militant with the Islamic Jihad militant group who had launched rockets toward Israel. Separately, Islamic Jihad claimed that one of its militants was killed with his mother and four siblings, but Al-Kedra said they were all civilians.

Israel and Hamas are bitter enemies and have fought numerous times over the years. But until recently they had been observing a truce that ended the previous hostilities in 2012.

Tensions have been rising since the kidnapping of three Israeli teenagers in the West Bank on June 12. Israel accused Hamas of being behind the abductions, although it provided no proof.

Israel then launched a crackdown on the group's members in the West Bank and arrested hundreds of people. Hamas, which controls Gaza, responded by stepping up rocket fire.

The situation deteriorated last week after the bodies of the three were found, followed a day later by the abduction of Palestinian teenager in Jerusalem — who was later found burned to death in what Palestinians believe was a revenge attack. Six Jewish Israelis were arrested in the killing.

It was a sharp contrast to the large number that hit Israeli cities the night before, setting off air raid sirens in Jerusalem, Tel Aviv and other areas of the country.

In amateur video obtained by The Associated Press, guests at an outdoor wedding in the city of Holon, near Tel Aviv, ran screaming for cover as a rocket was intercepted in the sky, blowing up. The bride and groom rushed down the aisle as a second rocket whizzed above.

By early Wednesday, air raid sirens sounded in Tel Aviv and Israel's south, and the army said two rockets were apparently intercepted above the central Israeli city by an anti-missile battery. In total, at least seven rockets were fired toward Israel on Wednesday, and the "Iron Dome" anti-missile system intercepted about half of them mid-air, the army said. There were no reported injuries.

Lerner, the army spokesman, told reporters that the military's aim was to take a "substantial toll" on Hamas and to deplete its rocket capabilities. He said the army would gradually ramp up its strikes on Gaza.

"The organization is going to pay for its aggression. It is literally holding us hostage with its rockets," Lerner said. "The country is not willing for this situation to continue."

About 2,000 people attended a funeral for eight Palestinians, including at least one militant, four adults and two children, who were killed Tuesday.

In the attack, an airstrike flattened the home of a Hamas militant in the southern Gaza town of Khan Younis. Israel's military said it had called the home shortly before the airstrike to warn civilians to leave.

A security official said the army has been telephoning homes, or firing small projectiles dubbed "knock on the roof," to warn civilians to leave buildings before demolishing homes. The official said the army also warns militants about such attacks if civilians are with them.

Hamas is far weaker than the last round of fighting with Israel in 2012.

At the time, Egypt was governed by the Muslim Brotherhood, Hamas' close ally. Following its ouster in 2013, Egypt's new government became hostile to Hamas and closed a network of smuggling tunnels used by the group as an economic lifeline, and as a way to smuggle in rockets.

An Israeli government official, speaking on condition of anonymity because he was discussing Israeli tactical strategy, said Israel could make more significant achievements against Hamas now than in previous rounds of fighting.

"Things are different now," the official said. "Their ability to rebuild their arsenal is far more limited."