President Donald Trump on Monday repeated his insistence that Iran will not be allowed to obtain a nuclear weapon.

Writing in all-caps, the US leader tweeted: "IRAN WILL NEVER HAVE A NUCLEAR WEAPON!"

The tweet came a day after Tehran announced it was further winding down observance of parts of an international deal struck to ensure that the country does not secretly develop a nuclear weapon under cover of its civilian nuclear industry.

Trump withdrew the United States from the 2015 deal negotiated under his predecessor Barack Obama.