Picture taken on January 11, 2009 shows that Israel's Prime Minister Ehud Olmert (R) and Foreign Minister Tzipi Livni attend the weekly cabinet meeting in Jerusalem. Israeli Prime Minister Ehud Olmert Saturday evening declared a unilateral ceasefire in the Hamas-ruled Gaza Strip, beginning from 2 a.m. (0000 GMT) Sunday.

JERUSALEM, Jan. 17 (Xinhua) -- Israeli Prime Minister Ehud Olmert Saturday evening declared a unilateral ceasefire in the Hamas-ruled Gaza Strip, beginning from 2 a.m. (0000 GMT) Sunday.

The declaration came shortly after Israeli security cabinet voted in favor of a unilateral ceasefire in Gaza, where Israel Defense Forces (IDF) Cast Lead Operation had been going on in the past three weeks, killing more than 1,200 Palestinians.

"We have reached all of our objectives in Gaza," said Olmert at a press conference in Tel Aviv, adding that Hamas has been dealt a heavy blow, and Hamas leaders are now in hiding.

Most rocket launching areas in Gaza are now controlled by the IDF, said the prime minister, adding "No doubt that without Cast Lead Operation, we would not have reached our goals."

Olmert said that if Hamas ended its rocket fire on Israel, the IDF would leave Gaza. But he did not say the exact time for the withdrawal.

Hamas had underestimated Israel's decisiveness, and was still not fully aware of how badly it had been damaged, said the prime minister, noting that "Our fight is not with the people of Gaza."

"We reached agreements with Egypt on fighting arms smuggling," he added.

Meanwhile, Israeli Defense Minister Ehud Barak warned that the IDF will stay in Gaza and restart the military operations if necessary.

"We will stop the fire but there is no guarantee that Hamas will do the same. The army will stay as needed and if Hamas continues to fire, the army will fire back severely and will be ready to follow and intensify its operations as necessary."