JERUSALEM: Israel is withdrawing some forces from Gaza to shift to more targeted operations against Hamas, and is partially returning reservists to civilian life to help the economy as the country enters the new year set for a prolonged war, an Israeli official said.

The official said the war will continue in the Palestinian enclave until the Islamist faction is toppled, adding that some of the troops withdrawn will prepare for a possible second front in Lebanon.

Since launching the Gaza offensive after the cross-border Hamas rampage of Oct. 7, Israeli officials have said they planned to wage it in three main stages. The first was intense shelling to clear access routes for ground forces and encourage civilians to evacuate. The second was the invasion that began on Oct. 27.

With tanks and troops having now overrun much of the Gaza Strip, largely asserting control despite Palestinian gunmen continuing their ambushes from hidden tunnels and bunkers, the military is moving to the third stage of the war, said the official, who could not be identified by name given the sensitivity of the issue.

"This will take six months at least, and involve intense mopping-up missions. No one is talking about doves of peace being flown from Shajaia," the official told Reuters, referring to a Gaza district ravaged by fighting.

Israel is also determined to recover the 129 still held in Gaza. Qatari- and Egyptian-mediated truce efforts have raised the prospect of some of them being freed.

Israel drafted 300,000 reservists for the war - an estimated 10% to 15% of its workforce. Some were quickly discharged, but government sources have said between 200,000 and 250,000 were still serving and absent from jobs or universities.

The official said the withdrawal was focused on reservists and designed to "re-energise the Israeli economy".

But the official said some of the troops pulled out of Gaza in the south would be prepared for rotation to the northern border with Lebanon, who Hezbollah have been exchanging fire with Israel in solidarity with the Palestinians.

Israel has warned that, if Hezbollah does not back down, a full-on Lebanon war looms. Both Hamas and Hezbollah are backed by Iran, whose allies in Syria, Iraq and Yemen have also been carrying out longer-range attacks against Israel.

"The situation on the Lebanese front will not be allowed to continue. This coming six-month period is a critical moment," the official said, adding that Israel would convey a similar message to a U.S. envoy conducting shuttle missions to Beirut.

In Gaza, the Israel-Hamas war has inflicted unprecedented devastation, with the health ministry reporting almost 22,000 fatalities, many of them civilian. Israel says it has killed more than 8,000 Palestinian fighters - suggesting that, by its own accounting, Hamas retains core personnel.

The Israeli military announced on Saturday it was sending some reservists home as part of what top commander Lieutenant-General Herzi Halevi has deemed a "reconfiguration" of forces.

"From the first moments of this war, we said it would take long," Halevi told troops on Tuesday. "Will we ultimately be able to say there are no more foes around the State of Israel? I think that is overly ambitious. But we will deliver a different security situation - safe and, as much as possible, stable too."