Gaza rocket fire struck a gas station and set it ablaze Friday in southern Israel, seriously wounding one person as rocket fire also came from Lebanon for the first time in the four-day offensive.

The explosion in Ashdod sent plumes of smoke high into the air. Israeli health officials said the blast wounded three people, including one in serious condition. Rocket fire continued in earnest from Gaza toward various locations in southern Israel.

In northern Israel, rocket fire struck near the Lebanese border and the military responded with artillery fire toward the source in southern Lebanon, military spokesman Lt. Col. Peter Lerner said.

The Lebanese military said three rockets were fired toward Israel around 6 a.m. and the Israelis retaliated by firing about 25 artillery shells on the area. Lebanese troops and United Nations peacekeepers later began searching the area, and the military said it was trying to find out who was behind the attack. No one was wounded on either side.

Southern Lebanon is a stronghold of the Shiite militant group Hezbollah, which has battled Israel numerous times. However, recent fire from Lebanon has been blamed on radical Palestinian factions in the area and Hezbollah has not been involved in the ongoing offensive. It has largely refrained from engaging Israel since a month-long war in 2006 when it fired thousands of rockets into Israel and was pummeled by Israeli airstrikes in response.

Lerner said Israel has suspected that Lebanese militants may try to join the fray as Israel exchanges fire with Islamic Hamas militants in Gaza. However, he said it was still unclear whether Friday's attack was "symbolic or something more substantial."

Gaza fighters have fired more than 400 rockets against Israel in the offensive. Israel's "Iron Dome" defense system has intercepted most aimed at major cities.

The rocket fire on Friday came hours after about 100,000 Gaza residents living in cities near the border with Israel were reportedly told Thursday to leave their homes ahead of anticipated military action by the Israeli army, according to Israeli media reports.

Israeli ministers have repeatedly hinted at a possible ground offensive over the past three days of airstrikes on Gaza, with troops massing on the border. Israel's Intelligence Minister Yuval Steinitz told Israel Radio on Thursday that the military "will have to take over Gaza temporarily, for a few weeks." Israel has called up 20,000 reservists.

Israel's military warned Gazans in Beit Lahia, Beit Hanoun and Abasan al-Saghira to flee, but residents are largely unable to leave the territory — though the border with Egypt was temporarily opened Thursday in order to let some injured people leave for treatment.

At least 88 people have been killed in three days of Israel's latest offensive on the Gaza Strip, and more than 50 of them were civilians, according to Gaza medical officials. Hundreds more have been injured.

In Israel, there have been no reports of any deaths resulting from hundreds of rockets sent from Gaza in recent days.

UNICEF said Thursday that among the Palestinian fatalities were 19 children. It warned that airstrikes and rocket attacks would continue to threaten the lives of young Palestinians and Israelis and called on both sides of the conflict to show "maximum restraint."

During a United Nations Security Council meeting held Thursday, a Palestinian envoy called on the body to "stop the carnage" in Gaza.

"Israel claims it is the only democracy in the Middle East, but it is attacking innocent civilians," envoy Riyad Mansour said. "Israel is perpetrating war crimes and state terror against civilians in Gaza."

Ron Prosor, Israel's ambassador to the U.N., told the council that Hamas, which controls Gaza, is "intentionally and indiscriminately" threatening 3.5 million Israelis. "No nation, no people and no government could tolerate this," he added.

U.N Secretary General Ban Ki-moon said Thursday that it was "unacceptable for citizens on both sides to permanently live in fear of the next aerial attack."

He added that an Israeli ground offensive and "an all-out escalation" was preventable only if Hamas stops firing rockets and mortars into Israel.

Mustafa Barghouti, a member of the Palestine Liberation Organization and a Palestinian legislator, warned that a ground assault could amount to "the most bloody massacre ever in this region."

In a conference call, he suggested that "thousands of lives" could be lost, "along with the potential imminent destruction of most of the infrastructure of Gaza."