Bashar al-Assad, the Syrian president, has urged all Arab nations to sever diplomatic ties with Israel because of the Gaza war.
Addressing leaders at Friday's emergency Arab summit in Doha, the Qatari capital, al-Assad declared that the Arab initiative for peace with Israel was now "dead".
Al-Assad said Arab countries should cut "all direct and indirect" ties with Israel in protest against its offensive in Gaza.
"Syria has decided that indirect peace negotiations with Israel will be halted," he said.
His comments were echoed by Khaled Meshaal, the exiled leader of Hamas, the Palestinian group that controls the Gaza Strip.
Meshaal also called on Arab leaders to cut all ties with Israel, stressing Hamas would not accept Israeli conditions for a ceasefire.
Egypt and Jordan are the only Arab countries who have signed peace treaties with Israel and have Israeli embassies.
Mauritania and Qatar suspended political and economic ties with Israel following Friday's summit.
Hamas has proposed a year-long, renewable ceasefire if Israel immediately ends its offensive in Gaza and lifts its crippling blockade of the territory.
Israel wants to ensure that Hamas, and other Palestinian fighters, will not be able to re-arm during any truce.
Recep Tayyip Erdogan, the Turkish prime minister, told delegates Israel should be barred from the United Nations while it continues to ignore UN demands to end the fighting in Gaza.
"How is such a country, which totally ignores and does not implement resolutions of the UN Security Council, allowed to enter through the gates of the UN?" he said.
Erdogan's comments came hours ahead of Friday's official visit to Turkey by Ban Ki-moon, the UN secretary general.
The Turkish leader also added his voice to widespread condemnation of Israel's bombing of a UN compound in Gaza on Thursday.
"The UN building in Gaza was hit while the UN secretary general was in Israel... this is an open challenge to the world, teasing the world," he said.
Diplomatic efforts to broker a ceasefire have intensified over recent days with emergency meetings being held in Qatar, Turkey, Kuwait and Egypt.
The UN secretary-general also visited the West Bank on Friday and Tzipi Livni, Israel's foreign minister, is flying to the US for talks.
However, Friday's emergency Arab summit in Doha, the Qatari capital, has highlighted the divisions within the Arab world, with Egypt and Saudi Arabia declining to attend, preferring instead to send delegates to a meeting of foreign ministers in Kuwait.
Amr Moussa, the secretary-general of the Arab League, admitted on Friday that the Arab nation's reaction to the war on Gaza was "in a very big chaos".
The Palestinian political factions Hamas, Islamic Jihad and the Popular Front for the Liberation of Palestine (PFLP) are also at the Doha summit.
Hashem Ahelbarra, Al Jazeera's correspondent in Doha, said the delegates in Qatar recognise the legitimacy of the Gazan factions, whereas Egypt, Saudi Arabia and Western nations have sidelined them from ceasefire talks.
"You have two camps: The so-called moderate Arab countries, Saudi Arabia, Egypt, Jordan, some Gulf monarchies like the UAE, and those who are trying to say that we totally disagree with the US attempt to implement a new Middle East."
Ahelbarra said the "moderate camp" is uncomfortable with Hamas's ties with Iran and suspects that the Iranian leadership is using some Arab countries to further its influence in the region.
- International force to stop weapons smuggling into Gaza
- Immediate halt to offensive
- Full withdrawal of Israeli troops from Gaza
- Re-open all crossing points into Gaza
- Lift Gazan economic siege
He said that the latter group believes it has the duty to convey the anti-war feeling of the Arab street and condemn Israel's actions.
Talks are continuing in Cairo over an Egypt-sponsored truce, with Amos Gilad, the Israeli chief negotiator, telling Egyptian officials Israel wants an open-ended ceasefire.
Israel is demanding that rocket fire from Gaza ceases and that an international force is established to prevent weapons being smuggled into Gaza.
Livni, due to arrive in Washington DC on Friday, will meet Condoleezza Rice, the outgoing US secretary of state, to discuss a potential US role in stopping weapons being smuggled into Gaza.
By Friday morning 1,133 Palestinians had been killed since Israel launched its offensive on December 27.