Talks on the possibility of a truce to end five days of violence in and around Gaza are under way, and a deal could be reached "today or tomorrow," a Palestinian official told Agence France Presse on Sunday.

"There are serious talks to reach a truce, and it is possible that understandings will be reached today or tomorrow," the senior official said.

Jordan's King Abdullah II called for an immediate halt to Israeli "aggression" against Gaza as he received Middle East Quartet envoy Tony Blair on Sunday, the royal palace said.

The monarch stressed "the need to speed up regional and international efforts to bring an immediate halt to Israeli aggression and military escalation," it said in a statement.

Syrian regime forces bombarded southern districts of the capital Damascus and clashes raged nationwide on Sunday.

In Damascus, government artillery bombarded the southern district of Al-Hajar al-Aswad, the Syrian Observatory for Human Rights said.

French Foreign Minister Laurent Fabius left Paris Sunday for Israel "to call on all the parties to stop the escalation and offer France's help to reach an immediate ceasefire," his ministry said.

During his one-day trip, the minister will meet with the Israeli authorities and Palestinian Authority President Mahmoud Abbas, his ministry said in a statement.

Israeli air strikes on Sunday killed 26 Palestinians in the bloodiest day so far of its massive air campaign on the Gaza Strip, as diplomatic efforts to broker a truce intensified.

With Egypt at the center of efforts to broker a ceasefire, Palestinian officials said it was possible a deal would be reached "today or tomorrow."

King Abdullah of Saudi Arabia, 89, has "successfully" undergone a new operation on his back, the royal cabinet announced Sunday.

The operation, to correct "a ligamentary slackening in the upper back" of the monarch, ended at dawn on Sunday, said a statement quoted by the official SPA news agency.

Egyptian President Mohammed Morsi called on his Argentine counterpart Cristina Kirchner to rally other Latin American leaders in support of stopping the violence in Gaza, Argentina said Saturday.

"The president of the Arab Republic of Egypt, Mohammed Morsi, contacted President Cristina Fernandez de Kirchner, to ask for her intervention, and through her the leaders of the region and the world, for an end of violence between Israel and the Palestinian faction Hamas, which rules the Gaza Strip," the government said in a statement on its website.

Egypt's President Mohammed Morsi said on Saturday his government was in touch with both Israelis and Palestinians and there were indications they could "soon" reach a truce, but there were no guarantees.

"There are some indications that there could be a ceasefire soon," Morsi said at a joint news conference with Turkish Prime Minister Recep Tayyip Erdogan, adding that there were still "no guarantees."

Arab League chief Nabil al-Arabi will head a delegation to Gaza in a show of solidarity after Arab ministers decided on Saturday to review their diplomacy towards Israel and show their support for the Palestinians.

The delegation will travel to Gaza "to affirm solidarity with the Palestinians," a League statement said after the foreign ministers' meeting. Arabi told reporters it would head for the enclave either on Sunday or Monday.

Hundreds of protesters demonstrated near the Israeli embassy in London on Saturday, waving placards and chanting slogans like "From London to Ramallah organize the intifada".

Speakers on a podium condemned the British government after Foreign Secretary William Hague said the Hamas regime running the Gaza Strip bore "principal responsibility" for the escalation of violence.