Iran said on Tuesday that the United States had violated a ceasefire after the US conducted what it called defensive strikes in southern Iran, while US Secretary of ​State Marco Rubio said that negotiating a deal to halt the conflict could "take a few days."

In a statement posted on its official news outlet Sepah News, Iran's Islamic Revolution Guard Corps (IRGC) warned that it reserves the "legitimate and definitive" right to respond to any violation of the ceasefire reached last month between Tehran and Washington by the "aggressive" US army.

Despite a ceasefire in place since early April, US Central Command said on Monday that it had carried out fresh strikes designed "to protect our troops from threats ​posed by Iranian forces."

Iran's foreign ministry said the US strikes in Iran's southern Hormozgan province, where Iranian media reported sounds ‌of explosions early on Tuesday, represented a "gross violation" of a tenuous ceasefire in place for nearly seven weeks.

The IRGC said its air defense forces have shot down an MQ-9 Reaper drone in the country's airspace.

The IRGC said its air defense forces have also detected and tracked an RQ-4 Global Hawk surveillance aircraft and an invading F-35 fighter jet, "which had entered Iran's airspace in continuation of the terrorist US army's interventionist adventurism in the region and aggressive behaviors," and forced them to flee by shooting at them.

Over the past weeks, the two sides reportedly exchanged several proposed plans outlining conditions for peace through Pakistan's mediation.

(With input from agencies)