Erez Crossing, Gaza Strip ? Palestinian gunmen and suicide car bombers staged an elaborate attack against a major Israeli checkpoint Saturday, in what militant groups called revenge for recent airstrikes targeting their members.

Four assailants and two Palestinian policemen were killed, but no Israeli soldiers were hurt.

The attackers used vehicles that looked nearly identical to Israeli army jeeps, complete with military markings, black-and-white army license plates and flashing lights on the roof. It was the latest surge of violence ahead of a proposed Israeli withdrawal from the Gaza Strip.

Militants said Saturday they were stepping up attacks to show they were forcing Israel out of Gaza. Israel was expected to intensify military strikes ahead of a withdrawal to avoid the impression of surrender. Seven Palestinians have been killed in targeted Israeli air strikes in Gaza City in the past week.

The attack began at 10 a.m. when a Palestinian taxi sped into the Erez crossing zone between Gaza and Israel and exploded just outside a heavily fortified army checkpoint.

Moments later, two more attackers in a jeep with Israeli military markings pulled up. One of the men jumped out and opened fire with an assault rifle. Troops fired back, killing the pair.

A second vehicle disguised as an army jeep blew up outside the crossing zone, apparently after Palestinian policemen guarding the Gaza side blocked its path. Two Palestinian policemen were killed.

The military said they were hit by the spray of shrapnel as the third car exploded, but Palestinian hospital officials said the two had gunshot wounds. Nineteen people, including police officers and taxi drivers, were wounded, two of them critically.

The three main Palestinian militant groups — Hamas, Islamic Jihad and Al Aqsa Martyrs’ Brigades — said they were behind the attack, calling it a joint “self-sacrifice operation.”

U.N. and Palestinian medical personnel inspect the damage at the Palestinian side of the Erez crossing point between Israel and the Gaza Strip. Saturday, Palestinian suicide bombers and gunmen attacked the site.