The relationship between the two states has deteriorated even further after the killing of Iranian top military commander Qasem Soleimani and Iran's retaliatory strikes on US military facilities in Iraq.

President Donald Trump said on Sunday he did not care whether Iran agreed to negotiate with the United States.

Earlier, White House National Security Adviser Robert O'Brien said that the "maximum pressure" campaign on Iran by strangling it with sanctions had been effective enough and would eventually press Tehran to negotiate.

"I think the maximum pressure campaign is working. Iran is being choked off, and Iran is going to have no other choice but to come to the table", O'Brien told Fox News Sunday.

After Iran conducted an attack on American military facilities in Iraq, as part of its "revenge" for the assassinated Gen. Soleimani, Trump said he would never ever allow the nation to possess a nuclear weapon. However, the US president said that he was still ready to make peace with Iran on condition it "changes its behaviour".

In 2018, Trump withdrew from the Joint Comprehensive Plan of Action (JCPOA), starting its economic campaign against Tehran by introducing tough sanctions on the nation. On 8 May, the first anniversary of the US' unilateral withdrawal from the agreement, Iran announced a gradual reduction of its JCPOA obligations. The deal was signed back in 2015 and envisaged Tehran's scaling back its nuclear programme in exchange for sanctions relief. 

Iran has repeatedly indicated that waging an economic war on Tehran and jeopardising the 2015 nuclear deal is not only harmful to the United States, but also for other nations involved and for international security on the whole.