The United States will help Israel and the Palestinians establish “fixed, defined parameters” for a permanent peace deal, Secretary of State John F. Kerry said Thursday, as troubled negotiations enter a new year and lurch toward a spring deadline for an accord.

Five months into the talks that he pushed both sides to begin last summer, Kerry is stepping into a more direct role as mediator. The immediate goal is an “agreed framework” to guide the final and most difficult phase of talks on how to settle the decades-old conflict, he said.

“This is not mission impossible,” Kerry said at the outset of his 10th visit to Israel as the United States’ top diplomat. He arrived as news spread that former Israeli prime minister Ariel Sharon is near death. The hawkish leader, who became a forceful advocate for a peace deal in his last years in office, has been in a vegetative state since a stroke in 2006.

Israeli Prime Minister Benjamin Netanyahu told Kerry that a recent spate of terrorist attacks has renewed doubt about Palestinian commitment to the peace effort. He accused Palestinian Authority President Mahmoud Abbas of helping to incite violence by warmly receiving Palestinians convicted of killing Israelis who, as part of the peace talks, were recently freed from prison.

“How can he say that he stands against terrorism when he embraces the perpetrators of terrorism and glorifies them as heroes?” Netanyahu said, standing alongside Kerry.

The interim agreement Kerry seeks would clarify positions, set out issues to be decided in a final deal and bind both sides to terms for resolving them. It would not contain specifics, U.S. officials have said, but would touch on all the tough topics — borders for Palestine, security for Israel and the fate of Palestinian refugees and East Jerusalem.

The agreement would be a milestone on the path to the permanent peace treaty Kerry wants to secure by the end of April, and a way to show skeptics that the talks are making headway.

“It would create the fixed, defined parameters by which the parties would then know where they are going and what the end result could be,” Kerry said. The United States is ready to propose its own ideas for bridging the deepest divisions, officials said.

Even before his arrival, Kerry appears to have won at least one small, but probably temporary, concession from Israel. Netanyahu’s government delayed publication of plans to build 1,400 housing units in the Israeli-occupied West Bank and East Jerusalem, at least until Kerry departs Sunday. By postponing the announcement, Netanyahu avoided embarrassing his high-profile guest and frequent dinner companion.

In 2010, Israel announced settlement building just as Vice President Biden arrived in the country. Biden took the move as an affront, calling it “precisely the kind of step that undermines the trust we need right now.”

What to do about existing Jewish settlements — which ones to keep within Israel and which ones to surrender to a future Palestine — is a core issue in past and present peace negotiations. The settlements house about 500,000 Israelis and sit on land that the Palestinians want for a future state, with East Jerusalem as its capital. They are illegal under international law, although Israel disputes this categorization.

Kerry has called the settlements “illegitimate.”

Dani Dayan, chief foreign envoy of the pro-settlement Council of Jewish Communities in Judea and Samaria, said it is his understanding that the new construction will be announced after Kerry leaves.

Netanyahu’s coalition government has linked such announcements to the freeing of Palestinian prisoners serving long sentences for killing Israelis. Israel agreed to release four groups of 26 prisoners in an effort to begin the talks last summer. It announced settlement construction immediately after the first two releases. U.S. officials leaned on the Netanyahu administration not to do the same when the third group of prisoners went free.

The latest prisoner release was extremely unpopular with Israelis, but the men were greeted by Palestinians as patriots.

“If Israel can’t release Palestinian political prisoners, who should not be in jail in the first place, without then building settlements, then what confidence can I have that Israel will evacuate Israel settlements when it comes to it?” said Diana Buttu, a Palestinian analyst and former legal adviser for the Palestinian negotiating team. “There is . . . a lot of skepticism on the Palestinian side.”

Israelis, too, are suspicious. Defense Minister Moshe Ya’alon was quoted in local media accounts telling a group of business leaders last week: “Don’t delude yourselves. We don’t have a partner on the Palestinian side for a two-state solution.”

Kerry thanked Netanyahu on Thursday for following through with the prisoner releases but also praised Abbas for sticking with the talks when many Palestinians are advising him to walk away.

Chief Palestinian negotiator Saeb Erekat has accused the Israelis of “foiling the efforts of Kerry,” and suggested that the Palestinian Authority seek redress at the United Nations and press war-crime charges against Israel at the International Criminal Court in the Hague. Erekat was especially upset about a proposal in the Israeli parliament, by members of Netanyahu’s party, that would have Israel annex the Jordan Valley, which accounts for about 25 percent of the West Bank.

Annexation proposals, however, are unlikely to go anywhere during the peace talks. Nor will Abbas allow the Palestinian Authority to go to the United Nations while negotiations continue.

The first casualty of the Israeli-Palestinian conflict in 2014 occurred Thursday. Saeed Jaser Ali, 85, from a Palestinian village in the northern West Bank, died at a local hospital hours after tear gas canisters fired to disperse protesters landed in his house, according to Palestinian media accounts.

Ruth Eglash contributed to this report