Donald Trump has warned Iran that "time is running out" to negotiate a deal on its nuclear programme following the steady build-up of US military forces in the Gulf.

The US president said a "massive Armada" was "moving quickly, with great power, enthusiasm, and purpose" towards Iran, referring to a large US naval force.

In response, Iran's mission to the UN said Tehran "stands ready for dialogue based on mutual respect and interests", but if pushed, it wrote in all capitals, it would defend itself and "respond like never before".

Iran insists its nuclear programme is entirely peaceful and has repeatedly denied seeking to develop nuclear weapons.

Trump's latest warning to Iran's leaders follows his promise that Washington would intervene to help those involved in the brutal and unprecedented crackdown on demonstrations in the country earlier this month.

"Help is on the way," he told protesters, before later changing his tune - saying he had been told on good authority that the execution of demonstrators had stopped.

The US-based Human Rights Activists News Agency (HRANA) says it has confirmed the killing of more than 6,220 people, including 5,858 protesters, since the unrest began at the end of December.

HRANA says it is also investigating another 17,000 reported deaths received despite an internet shutdown after nearly three weeks.

Another group, the Norway-based Iran Human Rights (IHR), has warned that the final toll could exceed 25,000.

However, Trump's warning on Wednesday appeared to focus more on Iran's nuclear programme.

"Hopefully Iran will quickly 'Come to the Table' and negotiate a fair and equitable deal - NO NUCLEAR WEAPONS," he wrote on Truth Social.

Trump said the naval force in the Gulf was larger than the one he sent to Venezuela before US forces seized the country's former leader Nicolás Maduro.

Trump added that this force was "ready, willing, and able to rapidly fulfil its mission, with speed and violence, if necessary".

Referring to the US strikes on Iranian nuclear sites last June, which was launched during Iran's 12-day war with Israel, Trump warned: "The next attack will be far worse! Don't make that happen again."

Earlier on Wednesday, before Trump's comments, Iranian Foreign Minister Abbas Araghchi said: "Conducting diplomacy through military threat cannot be effective or useful."

"If they [the US] want negotiations to take shape, they must certainly set aside threats, excessive demands and raising illogical issues," he said in televised remarks, translated by the AFP news agency.

Using open-source tools, BBC Verify has been able to track some of the US deployments to the area. A US defence official confirmed that a naval "armada" led by the USS Abraham Lincoln had also arrived in the Middle East.

The last time the US took action against Iranian nuclear sites was June last year, when it targeted three uranium enrichment facilities in Iran: Fordo, Natanz and Isfahan.

American officials then said the operation - codename "Midnight Hammer" - had significantly set back the prospect of Tehran building a nuclear weapon.

However, Hassan Abedini, the deputy political director of Iran's state broadcaster, claimed that Iran "didn't suffer a major blow because the materials had already been taken out" from the facilities.

In retaliation to the US strikes, Iran launched missiles on a US military base in Qatar - an attack described by Trump as "very weak" and "expected".