A ball of fire rises from an explosion on al-Zafer apartment tower following an Israeli air strike in Gaza City, in the northern Gaza Strip, Saturday, Aug. 23, 2014.

GAZA CITY, Gaza Strip - Israeli airstrikes leveled a seven-floor office building and severely damaged a two-story shopping center early Sunday, signaling a new escalation in seven weeks of Israel-Hamas fighting.

The strikes in the southern town of Rafah came just hours after Israel bombed an apartment tower in Gaza City, collapsing the 12-story building with 44 apartments.

The targeting of large buildings appears to be part of a new military tactic by Israel. Over the weekend, the army began warning Gaza residents in automated phone calls that it will target buildings harboring "terrorist infrastructure" and that they should stay away from those areas.

Meanwhile, Gaza militants continued to fire rockets and mortar shells at Israel, including at least 10 on Sunday, the military said.

Elsewhere, five more rockets were fired from Syria and fell in open areas in northern Israel. It was not immediately clear whether they were fired by pro-government forces or rebel groups.

Amid persistent violence, Egypt has urged Israel and the Palestinians to resume indirect talks in Cairo on a durable cease-fire, but stopped short of issuing invitations.

Several rounds of indirect talks between Israel and Hamas have collapsed, along with temporary cease-fires that accompanied them. The gaps between Israel and the Islamic militant group on a new border deal for blockaded Gaza remain vast, and there's no sign either is willing to budge.

In the town of Rafah, Israeli aircraft bombed the seven-story Zourab building which houses an office of the Hamas-run Interior Ministry. Witnesses said the building was leveled and that the strikes caused severe damage to nearby shops, homes and cars.

Another strike hit a nearby shopping center with dozens of shops, sparking a fire that gutted the two-story building. After daybreak Sunday, smoke was still rising from the site as shop owners inspected the damage. Windows and doors had been blown out in nearby buildings.

The military said the two buildings were attacked because they housed facilities linked to militants, but did not provide details. The Gaza City apartment tower toppled Saturday was targeted because a Hamas command center operated from there, the army said.

The U.N. estimates that more than 17,000 homes have been destroyed or damaged beyond repair since the war began on July 8. In some of the attacks, family homes with three or four floors were pulverized.

However, the weekend strikes marked the first time large buildings were toppled.

Since the fighting began, Israel has launched some 5,000 airstrikes at Gaza, while Gaza militants have fired close to 4,000 rockets and mortars, according to the Israeli military.

More than 2,100 Palestinians, including close to 500 children, have been killed, according to Palestinian health officials and U.N. figures. Israel has lost 64 soldiers and four civilians.

Israel says it is targeting sites linked to militants, including rocket launchers, command centers and weapons depots. The U.N. says about three-fourths of the Palestinians killed have been civilians.