However, the official stressed that no decision had been made.
Adding to the uncertainty, a source told Reuters that Vice President JD Vance was still in the US, denying reports that he was already on his way to Pakistan's capital Islamabad for talks.
With a two-week ceasefire set to expire, the senior Iranian official said it was "positively reviewing" its participation but no final decision had been made.
The comments conveyed a clear change of tone from earlier statements ruling out attendance and pledging to retaliate for US aggression.
The Iranian official said mediator Pakistan was making positive efforts to end the US blockade and ensure Iran's participation.
The ceasefire had appeared in jeopardy after the US said it had seized an Iranian cargo ship that tried to run its blockade and Iran vowed to retaliate.
Iranian Foreign Ministry spokesman Esmaeil Baghaei said on Monday that the US had shown it was "not serious" about pursuing the diplomatic process, and that Iran would not change its demands.
The US was hoping to start negotiations in Pakistan shortly before the ceasefire expires, with sweeping security preparations under way in Islamabad but Baghaei said the US was "insisting on some unreasonable and unrealistic positions".
A Pakistani security source said Pakistan's key mediator, Field Marshal Asim Munir, had told US President Donald Trump the blockade was an obstacle to talks, and that Trump had promised to consider ending it.
The US was hoping to start negotiations in Pakistan shortly before the ceasefire expires, with sweeping security preparations under way in Islamabad.
However, Iran's President Masoud Pezeshkian said that "unconstructive & contradictory signals from American officials carry a bitter message; they seek Iran's surrender."
"Iranians do not submit to force," he added on X.
The US military said it had fired on an Iranian-flagged cargo ship headed towards Iran's Bandar Abbas port on Sunday after a six-hour stand-off, disabling its engines.
US Central Command released video showing Marines descending ropes from helicopters onto the vessel.
The vessel is likely to have been carrying what the US deems dual-use items that could be used by the military, maritime security sources said on Monday.
Iran's military said the ship had been travelling from China and accused the US of "armed piracy," according to state media.
They said they were ready to confront US forces over the "blatant aggression" but were constrained by the presence of crew members' families on board.
China, the main buyer of Iranian crude, expressed concern over the "forced interception" and Chinese President Xi Jinping called for ships to resume passage through the strait as normal and for the conflict to be resolved through political and diplomatic channels, state news agency Xinhua reported.
Pakistan geared up to host the talks despite uncertainty over whether they would go ahead.
Nearly 20,000 security personnel have been deployed across the capital Islamabad, a government official and a security official said.
