An Iranian legislator on Tuesday offered a US$3m reward to "anyone who kills" US President Donald Trump to avenge the assassination of top general Qassem Soleimani.

American disarmament ambassador Robert Wood dismissed the reward as "ridiculous", telling reporters in Geneva it showed the "terrorist underpinnings" of Iran's establishment.

Ahmad Hamzeh, a little-known member of parliament, offered the bounty on behalf of the people of Kerman, the hometown and final resting place of the revered Soleimani, who was killed in an American drone strike in neighbouring Iraq on January 3.

"We will give three million dollars to anyone who kills Trump," Hamzeh, who represents Kahnouj county near the southeastern city of Kerman, was quoted as saying by the semi-official ISNA news agency.

He did not say if the idea of a reward had any official backing from Iran's clerical rulers. Hamzeh offered the money for the US president's assassination while speaking to the 290-seat parliament, or Majlis.

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Hamzeh also said Iran should start producing nuclear weapons and delivery systems to protect itself.

"If we had nuclear weapons today we would be protected from threats ... We should put the production of long-range missiles capable of carrying unconventional warheads on our agenda. This is our natural right," he was quoted as saying.

The United States and its Western allies have long accused Iran of seeking nuclear weapons. Tehran insists it has never sought atomic arms and never will, saying its nuclear work is for research and to master the process to generate electricity.

Under a 2015 nuclear agreement signed by Iran and world powers, Tehran received sanctions relief in return for curbing its nuclear activities.

Dying nuclear deal

Tensions have steadily escalated since Trump pulled Washington out of the historic nuclear accord and reimposed crushing US sanctions. In response, Iran has gradually rolled back its commitments to the deal.

The standoff erupted into tit-for-tat military attacks this month with the killing of Soleimani and Iran's missile barrage on a base in Iraq that housed American forces. The attack did not cause any US casualties.

Amid the crisis, Iran announced it will re-start its uranium enrichment work. On Monday, Iranian officials also threatened to pull out of the Non-Proliferation Treaty if the United Kingdom, France, and Germany were to bring nuclear-deal breaches to the UN Security Council and reimpose EU sanctions.

Trump withdrew from the Iran nuclear accord and launched a "maximum pressure" campaign seeking to halt all of Tehran's oil exports, which are vital to the country's struggling economy.