Palestinian fighters in the Gaza Strip have fired five rockets at Israel, one of which hit a school, according to Israeli officials.

Some of the rockets landed close to the Israeli coastal city of Ashkelon, officials said, straining a fragile ceasefire declared both by Israel and Hamas, which controls the Gaza Strip.

There were no casualties reported in the rocket attacks.

The ceasefire, declared on January 18, ended Israel's three-week military assault in Gaza which killed at least 1,300 Palestinians and 13 Israelis.

Since the end of Israel's Gaza offensive, Palestinian fighters have fired more than 100 rockets and mortar rounds at Israel.

Israel has also carried out several air raids targeting alleged fighters, weapons caches and smuggling tunnels beneath the Gaza-Egypt border.

Egypt has been struggling to mediate a more permanent ceasefire deal between the two sides in recent weeks, but the talks have shown little sign of progress.

Separately, Al Jazeera has learnt that Mussa Abu Marzuk, Hamas's second-in-command who lives in exile in Syria, entered the Gaza Strip via the Rafah crossing from Egypt on Friday.

Abu Marzuk, one of the main founders of Hamas in the 1980s, had been attending reconciliation talks with other Palestinian factions in Egypt.

An Egyptian terminal official confirmed the visit, while Hamas would neither confirm nor deny that Abu Marzuk had entered the Palestinian territory.