Death toll in Gaza reaches 121.

Nidal al-Mughrabi and Ori Lewis

GAZA/JERUSALEM July 12 (Reuters) - Israel deployed its eighth missile defense battery on Saturday to defend its cities from longer-than-expected attacks by militants in Gaza, while Israeli forces shelled positions in the Palestinian enclave for the fifth consecutive day, killing 15 people, according to medics. Israel maintained the possibility of a ground offensive in Gaza, despite international pressure to negotiate a ceasefire. The conflict has killed 121 people in the Gaza Strip since Tuesday. Residents said a mosque in the center of the Gaza Strip was bombed and reduced to ruins. Israeli military officials said the site housed an arms cache.

Residents spray-painted the mosque walls with the words: "We will prevail, despite your arrogance, Netanyahu," referring to the Israeli prime minister.

Asked if it's possible the conflict could shift from being an aerial battle to a ground war in Gaza to stop militants from continuing to fire rockets toward Israel, Israeli Prime Minister Benjamin Netanyahu replied: "We are considering all possibilities and preparing for all possibilities."

"No international pressure will stop us from acting with full force," the prime minister told reporters in Tel Aviv on Friday, a day after speaking by phone with U.S. President Barack Obama about the most violent moment in the conflict in almost two years.

Doctors in Gaza say that at least 81 civilians, including 25 children, are among the 121 killed in the airstrikes. According to the same doctors, three militants and 12 other people, including two women with special needs at a rehabilitation center and a 65-year-old man, were killed in an airstrike on Saturday.

Israel is determined to end the rocket attacks, which intensified last month after the arrest of hundreds of Hamas activists in the West Bank following the kidnapping of three Jewish teenagers who were later killed.