A senior Iranian official said ships violating the new zone would be sanctioned.
President Donald Trump announced "major combat operations" against Iran on Feb. 28, with massive joint U.S.-Israeli strikes targeting military, government and infrastructure sites.
Delegations from the U.S. and Iran entered negotiations in June aimed at a war-ending deal based on a memorandum of understanding signed by both countries.
The U.S. and Iran have nonetheless continued to exchange strikes, with the strategic Strait of Hormuz as the primary flashpoint. Trump said in August that the U.S. would launch a "crushing economic operation" to force Tehran into submission.
Iranian Foreign Ministry spokesperson Esmaeil Baqaei told reporters at his weekly press conference on Monday that a Qatari delegation was in Iran on Sunday "to help reduce tensions," and that an Iranian technical delegation had visited Qatar recently.
-ABC News' Victoria Beaule and Morgan Winsor
Overnight Israeli strikes in southern Lebanon killed at least 11 people -- among them two children -- and wounded five others, according to reports by the Lebanese state news agency NNA.
The deadly strikes occurred in the town of Kfar Rumman in the south of the country, NNA reported. Nine people were killed in an airstrike on a residential building and two people were killed in a drone strike on a car, NNA said.
There were strikes in several other towns in southern Lebanon overnight, including in Deir Zahrani, where the Israeli military issued an evacuation warning ahead of a strike on a building.
Israel has not commented on the strikes in Kfar Rumman.
-ABC News' Ghazi Balkiz and Victoria Beaule
Mohsen Rezaei, the secretary of Iran's Supreme National Security Council, said on Sunday that a restricted zone will be announced in the coming days "outside" the Strait of Hormuz, in comments carried by Iranian state media.
"We're making changes," Rezaei said. "In the coming days and weeks, we're going to announce a restricted prohibited zone outside the Strait of Hormuz, which begins from the blockade line of the U.S. Navy, including the Strait Of Hormuz, and extends to the Persian Gulf from the other side."
Few details were given on the plan, but Rezaei said any ship that enters the zone "with the intention of crossing the Strait of Hormuz" will be put on a sanctions list.
-ABC News' Jamie Dorrington
Mohammad Bagher Ghalibaf, Iran's chief negotiator and the speaker of the country's parliament, said in a speech posted to Telegram on Sunday that "the era of 'proportionate responses' is over."
The recent Iranian strikes targeting U.S. bases in the Middle East were "only the beginning," Ghalibaf said.
"The rules of the game have changed, and from now on, any transgression against the interests and security of Iran will receive a 'faster, heavier, and more painful' response," Ghalibaf said.
-ABC News' Rashid Haddou
