UN Secretary-General Ban Ki-moon on Saturday urged Hamas to stop firing rockets after Israel announced unilateral ceasefire.

He said that Israel's ceasefire "should be the first step leading to the full withdrawal of Israeli troops from Gaza," adding that he wanted the withdrawal "as soon as possible".

Hamas militants also needed to do their part to bring an end to the violence by halting their rocket attacks against southern Israel, he said.

Ban is on a week-long Mideast diplomatic tour to call for respect to a Jan. 8 UN Security Council resolution on ceasefire.

Ban has been calling for an immediate ceasefire since the Israeli offensive against Hamas began on December 27.

Israeli Prime Minister Ehud Olmert Saturday evening declared the unilateral ceasefire in the Gaza Strip, beginning from 2:00 AM (0000 GMT) on Sunday, but Israeli troops will remain in the strip.

However, Islamic Hamas movement's armed wing al-Qassam Brigades vowed to continue resistance shortly after Israel declared the unilateral ceasefire.

In a statement sent to reporters, al-Qassam Brigades said " The declaration of Olmert showed Israel is defeated before the Palestinian armed resistance," and "the Israeli declaration of unilateral ceasefire is an evidence of the occupation failure to achieve victory in Gaza."

Al-Qassam Brigades also said they "will continue resistance as long as the occupation of Gaza continues and the blockade is imposed."

Israeli Defense Minister Ehud Barak has warned that if Hamas continues to fire, the Israeli army will fire back severely and will be ready to follow and intensify its operations as necessary."