The UN Secretary General Ban Ki-moon on Thursday called on Israel and Palestinian militants in Gaza to maintain their ceasefire deal, albeit fragile.

At a news conference during his brief visit to Gaza, Ban also urged Israel to open more commercial crossing points with Gaza, which he said are essential "for the continued progress for the people of Gaza."

Israel imposed a closure on Gaza after the Islamic movement Hamas took over the territory in 2007.

Ban inaugurated a housing site which the UN Relief and Works Agency (UNRWA) had been building for the past few years. The project was interrupted by the Israeli closure but was resumed in 2010 thanks to the easing of some restrictions.

Speaking of efforts to alleviate the blockade, Ban said that " more needs to be done," adding that more crossings for shipping in building materials are "the ABC's of construction."

On the housing site, where Ban made an earlier visit in 2010, 151 units have been completed and the construction of another 449 is underway.

When the UN chief entered Gaza earlier on Thursday, relatives of some Palestinian prisoners threw shoes and sticks at his convoy for not agreeing to arrange a meeting with them. In response, Ban said "I fully share their concerns and frustrations and this is why I'm here."

Ban's visit aims to push the Palestinians and Israel to resume their peace talks that has been stalled since 2010. He urged the two sides to return to the negotiating table and demanded that Israel create the suitable political atmosphere for direct talks.