Iran said it will step up efforts to tackle problems created by U.S. sanctions that are crippling its economy.
A senior Iranian official also warned of a “painful response” if it comes under further attack.
Six months after U.S.-Israeli strikes on Iran launched the war, the conflict appears to be at a stalemate.
A preliminary ceasefire accord reached in June has unravelled, and little progress has been made in diplomatic efforts to get the peace process back on track.
After a pause in military action for much of August, tit-for-tat strikes have resumed with U.S. Central Command saying it hit three Iranian tankers on Saturday after Iran’s Islamic Revolutionary Guard Corps launched ballistic missiles at two U.S. Navy ships.
Following the attacks, Iran’s Parliament Speaker Mohammad Baqer Qalibaf said on Sunday that the U.S. should understand that the rules of the game have changed “before it is too late”.
“From now on, any attack against Iran’s interests and security will receive a faster, heavier and more painful response,” he said in a speech published on his Telegram channel.
A restricted zone would be announced outside the Strait of Hormuz in coming days, Mohsen Rezaei, the secretary of Iran’s Supreme National Security Council, said on Sunday, according to state media.
He added that the zone would include areas in the Gulf.
Few details were provided on the plan initially, but Rezaei said any ship entering the new zone would be added to a sanctions list.
Tehran has shown it retains the capability to attack U.S. interests in neighbouring countries and to shut down oil flows through the Strait of Hormuz, through which a fifth of global oil supplies flowed prior to the conflict.