Syrian President Bashar al-Assad on Sunday said it is necessary that ceasefire in the Gaza Strip should be accompanied with the withdrawal of Israeli forces from the strip, the official SANA news agency reported.

Assad made the remarks while meeting with visiting UN Secretary General Ban-Ki Moon, in which he also urged to lift the siege permanently and open all crossings at the same time.

The Syrian leader emphasized the importance of the United Nations to shoulder its full responsibilities and perform its role under the UN Charter, especially in light of Israeli use of internationally prohibited weapons in Gaza including phosphorus bombs.

He also called for collaboration of international efforts to deliver emergency humanitarian aid and help reconstruction in the Gaza Strip.

In turn, Ban appreciated the "positive and important" role Syria is playing in the region, affirming commitment to do everything possible to bring peace to the Middle East in accordance with relevant international resolutions and the land-for-peace principle, SANA said.

Ban concluded his brief visit and left for Egypt's Red Sea resort of Sharm el-Sheikh to attend an international summit on the Gaza crisis, which would also be attended by a number of European and Arab leaders.

Also on Sunday, exiled deputy chief of Hamas' politburo Mussa Abu Marzouk announced here a one-week ceasefire in Gaza to allow Israeli soldiers to withdraw, urging the opening of all the border crossings to let humanitarian aid and basic goods enter into Gaza.

Marzouk claimed that Israel has failed in its offensive to impose conditions on the resistance and the Palestinian people.

The Palestinian movements "are ready to cooperate with any efforts, especially those of the Egyptians, Turks, Syrians and Qatar is, to reach an agreement that meets our known demands, which are a permanent lift of the blockade and the opening of all the crossing points, including the Rafah crossing," said Marzouk.

Earlier in the day, Hamas, the Islamic Jihad (Holy War) and some other Palestinian factions as well as their armed wings also announced in Gaza they accepted a ceasefire with Israel and give Israel a one-week ultimatum to end its military occupation in the strip.

The announcement came hours after Israeli Prime Minister Ehud Olmert declared a unilateral ceasefire that took into effect at 2 a.m. (0000 GMT).

More than 1,240 Palestinians have been killed in the impoverished Gaza Strip and over 5,300 wounded since the launch of the Israeli raid on Dec. 27, 2008, which it said was aimed at revenging Hamas rocket and mortar attacks.