JERUSALEM — The Middle East was on the verge of war last night after Hamas threatened to renew suicide bombing on Israel. It did so after Israel launched air and ground attacks on the Gaza Strip.

“All options are open, including martyrdom operations [suicide attacks],” Abu Obeida, a spokesman for the military wing of Hamas, said.

Three Palestinian Arab fighters and three civilians were reported to have died in a wave of Israeli air strikes.

The Israeli army insisted that all were legitimate terrorist targets, although Palestinian Arabs reported one of the vehicles hit was a rubbish truck containing three civilians, a father and two teenage sons.

All three were killed. Because of security concerns, it was not possible to reach the area to check their status.

Israel added yet more military pressure when it sent tanks and a small ground force about a mile into northern Gaza before they apparently dug in for the night.

It was a clear show of strength but was not expected to lead to the sort of large-scale ground incursion that was seen in Gaza during the Second Intifada.

As the security situation deteriorated, Washington and London appealed for both sides to avoid all-out combat.

Secretary of State Rice telephoned Prime Minister Olmert as well as the Palestinian Authority president, Mahmoud Abbas, to discuss the situation.

Israel acted after Hamas fired scores of Kassam rockets across the Gaza perimeter, mostly hitting the Israeli town of Sderot, injuring six people and causing hundreds of civilians to flee. The Hamas barrage, the largest in months, appeared to be a ploy to provoke an Israeli response.

After days of fierce factional fighting with Fatah, in which 41 Palestinian Arabs died, Hamas believed a tough Israeli response might force the two rival groups to overcome their differences and unite against a common enemy.

Khaled Meshaal, the Hamas leader exiled to Syria, reflected this thinking when, hours after Israel launched its retaliatory attacks, he heralded the “historic opportunity” for the two factions to join together.

After four days of bloodletting between the two factions there was a noticeable reduction in fatalities yesterday although three people died in fighting at a funeral of one of the victims who died on Wednesday.

If Hamas was seeking to provoke a tough response from the Israelis, Tel Aviv obliged with its first air strikes in central Gaza City since last November’s cease-fire was declared.

A building used by Hamas was first to be hit. Later, Israeli helicopters launched attacks on vehicles that Israel said were ferrying Kassam rockets to launch positions.

A worsening barrage of Kassams has been landing in Israel since Monday with Hamas claiming responsibility.

By last night, more than 70 Kassams had landed. While there have been no Israeli fatalities, there was a direct hit yesterday on a school in Sderot, only six miles from Gaza.

Despite the criticism of his government’s handling of last year’s war in Lebanon, Mr. Olmert was fully aware that the Israeli public expected him to respond forcefully to the rocket attacks.

His chief spokesman, Miri Eisin, said Israel had shown restraint but could no longer allow the rockets to go unanswered.

In Washington, a State Department spokesman praised Israel for showing restraint.

The violence meant hopes faded for an early release of Alan Johnston, the BBC’s correspondent, who passed his 45th birthday still missing after being kidnapped on March 12 in Gaza City.