Former UN secretary general Ban Ki-moon said Israel's treatment of Palestinians “may constitute apartheid” during a three-day visit to the region.
Mr Ban, who is on a three-day visit to the region, said he was concerned that the chance of a two-state solution to the Israel-Palestinian conflict was “fading away”.
His visit coincided with a sharp increase in deadly violence in the West Bank.
Expanding Jewish settlements in the occupied West Bank and tighter restrictions against Palestinians have made the situation worse than when he was head of the world body from 2007 to 2016.
“I think the situation has worsened,” Mr Ban said. “I’m just thinking that, as many people are saying, that this may constitute apartheid.”
The comments come after the US ambassador to Israel, Tom Nides, said the Biden administration would “not stand by and watch settler violence occur”.
“No one should have to worry about a rogue army,” he said at a Tel Aviv gathering of young Israelis and Palestinians organised by the Geneva Initiative.
“My heart breaks for the families who lost a loved one 48 hours ago. We need to make sure that justice is done properly.”
Mr Ban was in the region on behalf of The Elders, a group of global leaders that engages in peacemaking and human rights initiatives around the world.
Along with the group's chairwoman, former Irish President Mary Robinson, he met with Israeli and Palestinian leaders and civil society, AP reported.
In apartheid South Africa, a system based on white supremacy and racial segregation was in place from 1948 until 1994.
“It’s clear that now we have a one-state rule and in fact it’s worse than that under the current government,” Ms Robinson said.
She said the group met with Israel's ceremonial president Isaac Herzog and opposition leader Yair Lapid, but Prime Minister Benjamin Netanyahu declined a meeting, as he has done in the past.
Israel rejects apartheid allegation
Rights groups in Israel and abroad have accused Israel and its 56-year occupation of the West Bank of moving towards an apartheid system that they say gives Palestinians second-class status and is designed to maintain Jewish hegemony from the Jordan River to the Mediterranean Sea.
The Rome Statute of the International Criminal Court defines apartheid as “an institutionalised regime of systematic oppression and domination by one racial group over any other racial group”.
Rights groups point to discriminatory policies within Israel and in annexed east Jerusalem, Israel’s blockade of the Gaza Strip, which has been ruled by the Hamas militant group since 2007, and its occupation of the West Bank.
Israel exerts overall control over the West Bank, maintains a two-tier legal system and is building and expanding Jewish settlements that most of the international community considers illegal.
Israel rejects any allegation of apartheid and says its own Arab citizens enjoy equal rights.
Israel granted limited autonomy to the internationally recognised Palestinian Authority, which is based in the West Bank, at the height of the peace process in the 1990s and withdrew its soldiers and settlers from Gaza in 2005.
It says the West Bank is disputed territory and that its fate should be determined in negotiations.
The accusations of apartheid and Jewish supremacy have only heightened under Prime Minister Benjamin Netanyahu's government, which is composed of parties that oppose Palestinian statehood, support settlement expansion and the adoption of a hard line against Palestinian militancy.
