KIRYAT MALACHI, Israel — Israel and Hamas brushed aside international calls for restraint on Thursday and escalated their lethal conflict over Gaza, where Palestinian militants launched hundreds of rockets into Israeli territory, targeting Tel Aviv for the first time, and Israel intensified its aerial assaults and sent armored vehicles rumbling toward the Gaza border for a possible invasion.

Defense Minister Ehud Barak of Israel, expressing outrage over a pair of long-range Palestinian rockets that whizzed toward Tel Aviv and set off the first air-raid warning in the Israeli metropolis since it was threatened by Iraqi Scuds in the Persian Gulf war of 1991, said, “There will be a price for that escalation that the other side will have to pay.”

Early Friday, the Israeli military said it had called up 16,000 army reservists, as preparations continued for a possible ground invasion for the second time in four years. Mr. Barak had authorized the call-up of 30,000 reservists, if needed, to move against what it considers an unacceptable security threat from smuggled rockets amassed by Hamas, the militant Islamist group that governs the isolated coastal enclave and does not recognize Israel’s right to exist.

It was not clear whether the show of Israeli force on the ground in fact portended an invasion or was meant as more of an intimidation tactic to further pressure Hamas leaders, who had all been forced into hiding on Wednesday after the Israelis killed the group’s military chief, Ahmed al-Jabari, in a pinpoint aerial bombing. But Prime Minister Benjamin Netanyahu of Israel said he was ready to “take whatever action is necessary.”