He's visiting the Middle East to meet Israeli and Palestinian leaders in a bid to end a three-week wave of violence.
Arriving in Jerusalem, United Nations Secretary General Ban Ki Moon had a stark warning.
"Israelis and Palestinians stand on the brink of another catastrophic period of violence. We need to keep the situation from escalating into a religious conflict with potential regional implications."
Speaking alongside Mr Ban, Israeli Prime Minister Binyamin Netanyahu accused Palestinian leader Mahmoud Abbas of inciting violence against Israelis.
"President Abbas, unfortunately, has been fanning the flames. He said on September 16th (he means October 16), just few days ago, that he welcomes - quote - 'every drop of blood spilled in Jerusalem'. That's a quote. President Abbas has not condemned a single one of the 30 terrorist attacks on Israelis over the last month and he continues to glorify terrorists as heroes."
Mr Ban condemned recent random attacks on Israelis.
But he cautioned that any tightening of security measures in response to the violence needs to be done with care.
"If the use of force is not properly calibrated it may breed the very frustrations and anxieties from which violence tends to erupt. I urge Israel as a democratic state to guard against such incidents and to conduct thorough investigations when necessary."
Mr Netanyahu insists Israel is not using excessive force.
At least 46 Palestinians have been killed in the upsurge in violence.
At least eight Israelis have died.
Mr Ban said it was not too late to avoid a broader crisis, and urged renewed peace efforts that would realise Palestinian hopes for statehood and Israel's wish for security.
The Secretary General is due to hold talks with Mr Abbas in the West Bank city of Ramallah.
In a sign of growing international concern, United States Secretary of State John Kerry will also meet Mr Netanyahu in Germany this week and Mr Abbas later at an unspecified location in the Middle East.
"I look forward to these meetings as an opportunity to try to pull people back from a precipice, and try to move down a road, because everybody understands that in the end, it requires a political solution, it requires two states living side by side in peace with two peoples appropriately honoured with their countries, and with security."
