The army said the visit was at the invitation of Haykal's Pakistani counterpart but did not immediately provide further details on its purpose or duration.
The surprise visit is notable given the insistence by the United States - and by Lebanese leaders including the president - that ceasefire talks for Lebanon remain separate from US-Iran negotiations mediated by Pakistan.
It comes as Iran's government again warned neighbouring countries against making their territory available for potential US military operations against it.
"The countries in the region should observe the principle of good neighbourliness and not use their territory for aggressive actions against Iran," the Iranian foreign ministry said on Saturday.
The statement follows US attacks early on Saturday on radar installations in the Sirik region and on the island of Qeshm in the south of Iran.
"This attack was a clear violation of the April 2026 ceasefire and a military aggression against Iran's territorial integrity," the ministry said.
Iran called on the United Nations Security Council to respond to what it called the "obvious violation of the ceasefire" and the "illegal actions of the US," which it said endangered both regional and international peace.
Israel and the United States attacked Iran three months ago.
A ceasefire has technically been in place in the war since April 8.
Nevertheless, mutual attacks continue to occur.
The US military said it intercepted several missiles on Friday fired by Iran at Kuwait and Bahrain, which are allied with the US.
Iran's Revolutionary Guards said they had attacked US bases in Kuwait and Bahrain in retaliation for U.S. strikes and fired at four tankers trying to cross the strait without its permission.
Previously, the US military also reportedly intercepted four Iranian drones in the Strait of Hormuz area and subsequently attacked radar stations in Iran on the island of Qeshm and in the town of Goruk.
The US and Iran have been engaged in largely indirect negotiations for an interim deal to halt the three-month-old war that would leave issues including Iran's nuclear program to further negotiations.
But a deal has remained elusive as the two sides have periodically skirmished.
Iran wants access to billions of dollars in oil revenue, waivers on sanctions on crude exports, the lifting of a US blockade on its ports and leverage over the Strait of Hormuz.
Iran has largely blocked the waterway, where about a fifth of global oil traffic transited before the war.
Iranian state media reported that Mohsin Naqvi, the interior minister of Pakistan, arrived in Tehran on Saturday for talks with Iranian officials including Foreign Minister Abbas Araqchi.
A Pakistani source said Naqvi would carry a message from Pakistan to the Iranian Supreme Leader Ayatollah Mojtaba Khamenei.
with DPA
