Michele Chabin, Yousef Al-Helou and Janelle Dumalaon

Special for USA TODAY

JERUSALEM — Israeli forces launched a ground operation into the Hamas-ruled Gaza Strip on Thursday night after several hours of heavy rocket fire into southern and central Israel by Gaza militants.

After 10 days of heavy fighting, Prime Minister Benjamin Netanyahu ordered the Israel Defense Forces to destroy tunnels used by militants to launch attacks in Israel, a statement issued by Netanyahu's office said.

"Through terror tunnels such as these, Hamas terrorists infiltrated Israeli territory early this morning with the aim of carrying out mass terrorist attacks against Israeli citizens," the statement said.

The offensive came after a failed attempt by 13 militants to infiltrate Israel on Thursday through a tunnel under the Gaza-Israel border, only to be stopped by an Israeli strike at the mouth of the tunnel.

Hamas spokesman Fawzi Barhoum said Israel "will pay dearly" for the assault. "Hamas is ready for a confrontation," he said.

Not long after a heavy barrage of rockets was fired at Tel Aviv and other parts of the country, thousands of soldiers backed by tanks and huge DC9 bulldozers entered Gaza after 10 p.m., Israeli media said.

Israeli news stations reported that Israel began its operation by shelling northern Gaza. Channel 10 News reported that the air force stepped up its aerial strikes while the navy fired from the sea.

The late-night broadcasts showed northern Gaza lit up by flares from Israeli forces.

Shortly before the operation, the Defense Forces instructed Israeli residents in the south near the Gaza border to remain in their homes.

The goal of the operation is to target Hamas infrastructure, including tunnels, storage facilities, launching pads and any structures the group uses to launch its rockets, Lt. Libby Weiss, a Defense Forces spokeswoman told USA TODAY.

"We have a substantial amount of forces, though I can't specify numbers," Weiss said. "These include armored forces, infantry, artillery and aerial and naval support. This is not a time-bound operation. It's a goal-bound operation."

She said civilians are not the target, stressing that Israeli forces will continue to take measures to minimize civilian casualties.

Thousands of Israeli soldiers had massed on the border with Gaza in recent days, waiting for the order to go in. More may be coming.

The government has authorized the military to call up an additional 18,000 reserve soldiers, the Associated Press reported.

A Hamas official told the Associated Press that heavy Israeli shelling was hitting eastern Gaza, near the border with Israel. He said all border areas are under fire, and tank shells hit every minute. The official spoke on condition of anonymity in line with briefing regulations.

Late on Thursday, Reuters reported that while shelling was heavy along the easter border of the southern town of Rahah, there was no immediate sign that tanks were moving in.

Residents told the Associated Press the northern Gaza town of Beit Lahiya came under heavy Israeli shelling. "There is the sound of tank shells all the time," said Jamal Abu Samra, 42, a farmer in the area. He said his wife, six children, four brothers and their families were huddling on the ground floor of the family home.

"We don't have power since the afternoon so we are listing to the (battery-operated) radio to hear the news," he said.

He said the Israeli military sent text messages to residents urging them to leave the area. Abu Samra said he and his relatives decided to stay because they felt nowhere in Gaza is safe. "It is better to stay home than move anywhere," he said.

The ground offensive is the first major Israeli incursion in Gaza in more than five years. Israeli strikes have hit more than 2,000 targets in Gaza, and Hamas launched nearly 1,500 rockets at Israel, according to the Israeli military.

The cross-border battles have killed more than 220 Palestinians and one Israeli.

The incursion followed a brief lull Thursday to allow Gaza residents to stock up on food and other supplies.

Two hours into that cease-fire early Thursday, Israelis near the border were forced back into bomb shelters after rockets were launched at them. After that, the five-hour truce held until its precise end, when Gaza militants began launching at least 40 rockets and mortar shells into Israeli towns and cities. Sirens sounded as far north as Herzilya in the center of Israel.

Israel responded by launching two airstrikes at Gaza, the Associated Press reported.

Earlier Thursday, Egypt had pushed for a cease-fire to end the conflict that began July 8. Egyptian President Abdel Fattah al-Sisi met with Palestinian leader Mahmoud Abbas, who governs the West Bank, after Egyptian officials met with representatives of Israel and Hamas in Cairo.

Israel had accepted Egypt's call this week to halt the fighting, but Hamas rejected it, saying it wanted more concessions that include easing a blockade of Gaza by Israel and Egypt.

The United Nations Relief and Works Agency, which cares for Palestinian refugees, announced Thursday that it had discovered rockets hidden in a vacant Gaza school.

"UNRWA strongly condemns the group or groups responsible for placing the weapons in one of its installations," it said in a statement.

"This is a flagrant violation of the inviolability of its premises under international law," it said. The incident "endangered civilians, including staff, and put at risk UNRWA's vital mission to assist and protect Palestine refugees in Gaza."

Also Thursday, the Israeli Ministry of Defense said the murder of a 16-year-old Arab resident of East Jerusalem was a terror attack, for which three Jews were indicted on murder charges.

Muhammed Abu Khdeir was kidnapped July 2, and his burned body was discovered in a Jerusalem forest a few hours later. His murder, after the abduction and murder of three Israeli teens in the West Bank, sparked widespread Arab rioting in East Jerusalem and throughout Israel and precipitated the current fighting.

The move to designate Abu Khdeir as a terror victim "was made as a result of the indictment and the findings of the investigation, which point to the nationalist motive of his murder," the ministry said.

A 29-year-old man and two 17-year-olds, who have not been named, were indicted in the murder. The Shin Bet security services said the suspects confessed to the crime, which they said was to avenge the murder of the three Israeli teens, who were kidnapped June 12. Israel blames Hamas for that crime. The teens were buried the day before Abu Khdeir was killed.

The designation as a terror victim entitles Abu Khdeir's family to financial benefits provided by Israel's National Insurance Institute. Although many Arab families in Israel receive such benefits because of terror attacks carried out by Palestinians, the government rarely designates crimes committed by Jews as a terror attack.

Al-Helou reported from Gaza City, Dumalaon reported from Berlin. Contributing: Associated Press