Antonio Guterres also told journalists at United Nations headquarters in New York that international freedom of navigation must be respected "by all parties" in the Strait of Hormuz.

"There is no military solution to this crisis. Peace agreements require persistent engagement and political will. Serious negotiations must resume," he said.

Guterres said the ceasefire between the United States and Iran "must be preserved" -- referring to the two-week truce agreed last Wednesday after mediation by Pakistan.

The two sides held talks in Islamabad at the weekend but failed to reach an agreement. US President Donald Trump told the New York Post on Tuesday that a second round of Iran talks could happen in Pakistan "over the next two days."

The UN chief welcomed the start Tuesday of the first direct talks in decades between Israel and Lebanon -- a dialogue being held in Washington and opposed by pro-Iran Hezbollah, which is battling Israeli forces in southern Lebanon.

"Nobody expects that these talks today will solve all the problems, but I think it will be very important if these talks create the conditions to a change in the way the actors have been developing their activities," Guterres said.

"Until now, the truth is that Hezbollah and Israel have always helped each other to destabilize the government of Lebanon," he said.

Guterres also made a broader appeal for diplomacy and "restraint and responsibility," and for respect for international law which was being "trampled" around the world.

The UN chief warned that "lawlessness breeds chaos," suffering and destruction.