Iran's military has begun its annual drill in the coastal area of the Gulf of Oman near the strategic Strait of Hormuz.
This is even as the authorities continue their crackdown on anti-government protests that have been under way for more than three months.
The strait is located at the mouth of the Persian Gulf and is crucial to global energy supplies, with about a fifth of all oil traded at sea passing through it.
State TV reports have said commandos and airborne infantry would participate in the wargames, dubbed "Zolfaghar-1401", along with drones, fighter jets, helicopters, military transport aircraft and submarines.
It added that Iran's military is to fire missiles and air defence systems as well.
The manoeuvres are aimed at "improving readiness in confronting foreign threats and any possible invasion", the reports said.
Deputy Commander of Army for Coordination Affairs Rear Admiral Habibollah Sayyari said that exercise Zolfaghar-1401 started on Thursday night with the participation of various units of the army.
Ground, air, and naval forces of the army will attend the joint exercise to show self-confidence, power and sustainable security, Mr Sayyari added.
Iran regularly holds such drills to improve its defensive power and test weapons.
Since mid-September, Iran has been shaken by anti-government protests.
They were ignited by the death of 22-year-old Mahsa Amini who was detained by the country's morality police.
The demonstrations rapidly escalated into calls for an end to more than four decades of the country's clerical rule.