Hours after a cease-fire was declared Wednesday in Israel's conflict with Gaza, it appeared to be holding, an Israeli official said.

"We assumed it would take a while for the cease-fire to take hold," Israel's ambassador to the United States, Michael Oren, told CNN. "I understand now that it has taken hold. There hasn't been fire for a while and, of course, we are not firing, so there is a cease-fire."

His remarks came after an Israeli military spokeswoman, Lt. Col. Avital Leibovich, told CNN that five rockets had been fired from Gaza in violation of the cease-fire. Deputy Foreign Minister Danny Ayalon, in an interview with CNN, put the number of rockets at 12.

Wednesday's cease-fire followed eight days of violence along Israel's border with Gaza and nearly 150 deaths -- the vast majority of them Palestinian.

The cease-fire, announced in a joint news conference in Cairo with U.S. Secretary of State Hillary Clinton and Egyptian Foreign Minister Mohamed Kamel Amr, took effect at 9 p.m. (2 p.m. ET).

Gazans took to the streets, firing guns into the air in celebration of what they considered to be a victory over Israel's military.

The agreement calls for Israel to halt all acts of aggression on Gaza, including incursions and the targeting of people, according to Egypt's state news agency EGYNews. It also calls for the Palestinian factions to cease all hostilities from Gaza against Israel, including the firing of rockets and attacks on the border. Border crossings were to be opened Thursday night, and the movement of people and goods across them was to be eased, it said.

The agreement came after a day of negotiations that included Clinton, Egyptian President Mohamed Morsy and Palestinian officials.

Israeli government spokesman Mark Regev said the agreement calls for "complete and total cessation of all hostile activity initiated in the Gaza Strip."

"For us, that's victory. That's what we wanted," he said.

Prime Minister Benjamin Netanyahu warned of possible additional military action if the cease-fire fails to lead to long-term security. "But at this time, the right thing for the state of Israel is to exhaust this opportunity to obtain a long-term cease fire," he said.

Netanyahu thanked U.S. President Barack Obama for his "unreserved support" of Israel's actions.

It was the November 14 assassination by Israeli forces of Ahmed al-Ja'abari, the head of Hamas' military wing, that ignited the fighting.

Israel launched its offensive with a stated goal of ending the rocket attacks on southern Israel from inside Gaza by degrading the ability of Palestinians to launch such attacks.

"Their attempts backfired against them," said Khaled Meshaal, a Hamas political leader. "They wanted to destroy the infrastructure of the resistance of Hamas. They claim they have done so, and they have not. They are bankrupt."

He cited Israel's destruction of buildings and killings that included civilians. "This is their accomplishment," he said. "They have nothing else to show. And our rockets continued to strike them until the last minute."

Israel will hold Hamas responsible for any attacks from Gaza, whether conducted by that organization or any others, Regev said. He said the agreement reflects that understanding.

As he was preparing to return to New York from Tel Aviv, U.N. Secretary-General Ban Ki-moon said late Wednesday his biggest concern was for the safety of civilians, "no matter where they are. Innocent people, including children, have been killed or injured on both sides. Families on both sides were forced to cower in fear as the violence raged around them."

He said that more than 139 Palestinians had been killed, more than 70 of them civilians, and more than 900 were injured. In addition, some 10,000 Palestinians had lost their homes, he said, adding there was a critical need for humanitarian aid in the territory.

IDF's Leibovich dismissed such concerns. "There is no crisis in Gaza," she told CNN, adding that she had seen pictures Wednesday morning of markets filled with fresh produce. "I understand that some things are not convenient," she said.