Hamas will not attend the Non-Aligned Movement (NAM) conference in Tehran, Palestinian news sources close to the party reported Sunday.

According to Quds Press news agency, Hamas Prime Minister Ismail Haniyeh decided not to travel to Iran as a “quiet protest” over the Islamic Republic’s support for Syrian President Bashar Assad. In January, Hamas abandoned its Damascus headquarters over the bloody government crackdown on the popular uprising in Syria.

Palestinian sources said that Hamas’s attempt to heal the political divide with rival movement Fatah also led the Hamas leadership to decline the invitation to the summit, which it had initially accepted on Saturday.

The Palestinian Authority (PA) had threatened Sunday to withdraw from the conference and to call on other delegations to do the same if Haniyeh arrived as an official or nonofficial representative of the Palestinians.

Abbas’s secular, Western-backed Fatah party and the extremist Islamic Hamas are bitter rivals. Violence between the two sides in 2007 left the Palestinians divided, with Hamas taking control of Gaza and Fatah governing the West Bank. Repeated attempts for reconciliation have failed.

The US, EU, Canada, Israel and other countries classify Hamas as a terrorist organization. It came to power in Gaza in 2007 after national elections were followed by the violent overthrow of Fatah in the Strip.