Iran's foreign minister has said that the country is open to negotiations with the U.S. on the condition that all sanctions are lifted, a proposal that President Donald Trump quickly dismissed.

Foreign Minster Mohammed Javad Zarif told Germany's Der Spiegel magazine that he would 'never rule out the possibility that people will change their approach and recognize the realities,' in an interview conducted Friday in Tehran.

Although Zarif suggested Iran was still willing to talk, he reiterated his country's previous demand that first the U.S. would have to lift sanctions.

'For us, it doesn´t matter who is sitting in the White House, what matters is how they behave,' he said. 'The Trump administration can correct its past, lift the sanctions and come back to the negotiating table. We´re still at the negotiating table. They´re the ones who left.'

Foreign Minster Mohammed Javad Zarif suggested Iran was still willing to talk, but he reiterated his country's previous demand that first the U.S. would have to lift sanctions

In Washington, Trump rejected Zarif's remarks in a tweet. 'Iranian Foreign Minister says Iran wants to negotiate with The United States, but wants sanctions removed,' he tweeted, then added, 'No Thanks!'

Meanwhile on Saturday, Ali Asghar Zarean, an aide to Iran's nuclear chief, said Iran's enriched uranium stockpile has exceeded 1,200 kilograms (2,646 pounds), which is far beyond the 2015 nuclear deal between Tehran and world powers allowed.

'Iran is increasing its stockpile of the enriched uranium with full speed,' he said. The claim has not been verified by the U.N.'s nuclear watchdog.

There has been growing tension between Washington and Tehran since in 2018, when Trump pulled the United States out of the nuclear deal with Iran. The U.S. has since reimposed tough sanctions that have crippled Iran's economy.

Following the U.S. drone strike on January 3 that killed Revolutionary Guard Gen. Qassem Soleimani, Iran announced it would no longer abide by any of the deal's limitations to its enrichment activities.

It then retaliated January 8, launching ballistic missiles at two bases in Iraq housing American troops, causing injuries but no fatalities among soldiers there.

In Washington, President Trump quickly rejected Zarif's remarks in a tweet

Trump repeated his tweet dismissing negotiations in both English and Persian

In November, the International Atomic Energy Agency said Iran's stockpile of low-enriched uranium had grown to 372.3 kilograms (821 pounds) as of Nov. 3. The nuclear deal limited the stockpile to 202.8 kilograms (447 pounds).

Iran has routinely vowed to begin enriching its stockpile of uranium to higher levels closer to weapons grade if world powers fail to negotiate new terms for the nuclear accord following the U.S. decision to withdraw from the agreement and restore crippling sanctions. European countries opposed the U.S. withdrawal and have repeatedly urged Iran to abide by the deal.

Under the agreement, Iran agreed to limit its enrichment of uranium under the watch of U.N. inspectors in exchange for the lifting of sanctions.

Trump has maintained that the 2015 nuclear deal needs to be renegotiated because it didn't address Iran's ballistic missile program or its involvement in regional conflicts. The other signatories to the nuclear deal - Germany, France, Britain, China and Russia - have been struggling to keep it alive.

Zarif did suggest Iran was also still prepared for conflict with the U.S., though was not specific.

'The U.S. has inflicted great harm on the Iranian people,' he said. 'The day will come when they will have to compensate for that. We have a lot of patience.'