Abu Ali Mustafa, assassinated by a missile from an Israeli helicopter gunship yesterday, was a gentleman revolutionary. Generally well turned out in suit and tie, he was a soft-spoken man rather than a firebrand militant.

His real name was Mustafa Zebri, Abu Ali being his nom de guerre. He began working for the Palestinian cause in the late 1960s when Dr George Habash founded the Popular Front for the Liberation of Palestine (PFLP). The PFLP initiated resistance activity in the West Bank after its occupation by Israel in 1967. Many of its ardent young activists were caught, jailed and then deported by Israel.

The front's exiled wing also launched attacks on Israel across the Jordan and pioneered civilian aircraft hijacking as a means for gaining the world's attention for the Palestinian struggle.

But Abu Ali, who was 63 when killed yesterday in an Israeli helicopter gunship attack on his home, was not the mastermind of the spectacular hijacks which put the PFLP on the global political map: the hijack specialist was a mild-mannered physician called Dr Wad'ia Haddad, who died many years ago.

In 1970 Abu Ali became the deputy secretary-general of the PFLP and succeeded the ailing Dr Habash in the top post in July 2000.

I met him in Damascus several years ago when I interviewed Dr Habash for The Irish Times.

Born in the village of Araba near the northern West Bank town of Jenin, Abu Ali lived most of his life in exile, returning only in 1999.

From the outset, he opposed the 1993 Oslo accord on the grounds that Israel would not allow the Palestinians to establish a viable state in the West Bank and Gaza.

Instead the PLO/Palestine Authority would become Israel's surrogate. By the time he returned from exile, the Oslo process was in serious trouble but he did not, at that time, call for a return to armed struggle. Instead, he strove to place the diplomatic effort back in the hands of the international community.

It is unlikely that Abu Ali was responsible for the string of bombings and shooting attacks for which he is blamed by Israel. He was a returnee, an exile who settled back in his homeland; the military wing of the PFLP, now a tiny faction with the support of only 2-3 per cent of Palestinians in the West Bank and Gaza, is dominated by young Palestinians raised in the territories who do not take orders from ageing returnees.

Today's activists are not gentlemen revolutionaries but hard men, their steel tempered by the occupation and two insurrections.

While Abu Ali refused to meet Israeli politicians and peaceniks, he promoted dialogue between the dissident PFLP and the mainstream Fatah faction of President Yasser Arafat and with Islamic groupings. Abu Ali's objective was to unify the disparate secular and Islamist Palestinian factions.

His death may very well help forge the unity he sought in life. Islamic Hamas was the first group to vow vengeance for his assassination.

Fatah was quick to follow. Since the Palestinian uprising, the Intifada, erupted again 11 months ago, the 14 political factions in the Palestinian territories have worked together in national committees to co-ordinate resistance activities.

The killing of Abu Ali will drive home the understanding that survival depends on unity. It is expected that today's Palestinian general strike will be strictly observed.

SINCE Abu Ali was the most senior political figure among the 50 prominent people Israel has assassinated since last October, his death will have a greater resonance among Palestinians than earlier victims.

Although the PFLP has long rejected the policies of Yasser Arafat, it remains a respected component of the Palestine Liberation Organisation (PLO), the umbrella movement grouping the secular factions.

Therefore Palestinians see this killing as a direct attack on the PLO itself, the internationally recognised representative of their people. The assassination reverberated across the Arab world yesterday, eliciting condemnation from both governments and commentators.

The Jordanian Information Minister, Mr Saleh Qallab, castigated Israel and called on the international community and the superpowers to "put serious and efficient pressure on Israel" to end policies which "violate norms of international law". Palestinian refugee camps in Lebanon, Syria and Jordan mourned the slain Mustafa with demonstrations and readings from the Quran broadcast from the minarets of mosques.

His death is felt by ordinary Arabs because the PFLP has a special place in Arab hearts and minds. The front is the successor to the Arab Nationalist Movement (ANM), which was founded by Dr Habash in the 1950s.

The movement took the line that Palestine could be liberated only when the Arabs achieved unity. The ANM gave its support to the Egyptian president, Col Gamal Abdel Nasser, as the Arab leader most likely to secure this objective.

While the ANM retreated from the wider Arab scene after Nasser's defeat by Israel in 1967, the nationalist impulse it inspired remains a potent force today.

All the more so because Arab citizens are deeply disturbed by their governments' failure to extend strong diplomatic and financial support to the Palestinian Intifada.

Michael Jansen is a commentator on Middle Eastern affairs for The Irish Times