UN Secretary-General Ban Ki-Moon said Friday that although Israelis and Palestinians were engaged in peace talks brokered by the US, an “increasingly dangerous situation” on the ground could threaten future negotiations.

In remarks marking the “International Day of Solidarity with Palestinian People,” Ban said he was “alarmed by the increasingly dangerous situation on the ground. There has been an escalation of violence and incitement.” The UN-sanctioned observance has been marked since 1978.

Ban also criticized recent announcements by Israel of construction in West Bank settlements, calling them a “cause for grave concerns.”

“Announcements of thousands of new housing units cannot be reconciled with the goal of a two-state solution and risk the collapse of negotiations,” said the secretary-general.

Earlier this month, the Housing Ministry published tenders for the planning of some 20,000 settlement apartments — an unprecedented number — including 1,200 units in the controversial E1 corridor linking Jerusalem with Ma’aleh Adumim. Prime Minister Benjamin Netanyahu quickly ordered the tenders cancelled.

According to Housing Ministry statistics published Thursday, seven percent of new Israeli construction sites erected this year were located in the West Bank, and the number of building projects across the Green Line rose by nearly 130% compared to 2012.

Ban also slammed Hamas rocket attacks on Israel and the building of smuggling tunnels into Israeli territory, AFP reported.

Urging Fatah and Hamas to overcome divisions, Ban said “all parties must act in a responsible way and refrain from actions that undermine the prospects for successful negotiations,” adding that ”we cannot afford to lose the current momentum of opportunity.”

Earlier Friday, a senior Palestinian official said that peace negotiations with Israel have already failed, and that the prospect of freeing Palestinian prisoners from Israeli jails is all that was keeping the talks alive.

Fatah Central Committee Member Nabil Shaath, a close adviser of Palestinian Authority President Mahmoud Abbas, told Maariv that “we are committed to negotiations for a nine-month period and are waiting until all 104 prisoners are released.”

Israel agreed to release 104 Palestinian prisoners from Israeli jails in four waves as precondition to the talks, which began in late July. Over the past five months, Israel has released two waves of 26 prisoners apiece to the West Bank and Gaza Strip. The 21 men released to Ramallah last month were met with fanfare and celebration by thousands of Palestinians and Abbas.

Under heavy American pressure and intense shuttle diplomacy by US Secretary of State John Kerry, Israel and Palestinians resumed peace talks five months ago after a three-year hiatus in negotiations. Although leaks about progress in the talks have been rare, they have been marked by difficulties including an uptick in Palestinian attacks against Israelis and, as previously mentioned, increased settlement unit announcements.

Kerry is due back in the region next week to meet separately with Netanyahu and Abbas. During his last stay in Israel earlier in November, Kerry made pointed remarks to the Israeli press about the ongoing talks.

“If we do not resolve the issues between Palestinians and Israelis, if we do not find a way to find peace, there will be an increasing isolation of Israel, there will be an increasing campaign of delegitimization of Israel that’s been taking place on an international basis,” he warned.