The foreign minister of the Hamas-led Palestinian Authority walked out of talks in Malaysia in apparent protest at a senior Fatah official's arrival.
Mr Zahar may still attend some meetings
Mahmoud al-Zahar walked out of the Non-Aligned Movement meeting after Fatah's Faruq Qaddumi presented himself as head of the Palestinian delegation.
He added insult to injury by announcing he intended to "train" his Hamas counterpart in diplomacy.
The spat comes amid increasing tensions between Hamas and Fatah.
'I would train you'
Faruq Qaddumi was quoted as saying the umbrella organisation, the Palestinian Liberation Organisation, to which Fatah belongs, was the sole representative of the Palestinian people.
Hamas has been refusing to acknowledge the PLO as such.
Mr Qaddumi, who is currently in exile in Tunis, told reporters: "I have had 30 years of experience. This is the first day he is coming to such a conference.
"I told him, I would train you and then I will turn over the whole process to you. And you be the minister of foreign affairs."
The BBC's Jonathan Kent in Kuala Lumpur where the conference is being held, said Mr Zahar - who is 55 - appeared "less than impressed" at the comments.
Malaysia's foreign minister, Syed Hamid Albar, attempted to down play the row and said Mr Zahar would be attending 'bi-lateral' meetings.
The Middle East - including the row between Hamas and Fatah - is expected to dominate proceedings between the 116 developing nations.
It is hard enough as it is to persuade the NAM to agree a meaningful stand on anything controversial, our correspondent says.
So Malaysian hopes of pushing through a motion in support of the Palestinians can hardly have been helped by the spectacle of the two main Palestinian factions squabbling, he adds.
Palestinian leader Mahmoud Abbas has warned that internal power struggles among Palestinians are jeopardising the dream of an independent state.