Trump administration to 'substantially increase' Iran sanctions

President Donald Trump on Wednesday announced what he said would be substantial new sanctions against Iran in the first response to what US officials say was likely Iranian involvement in an attack on Saudi oil facilities.

"I have just instructed the Secretary of the Treasury to substantially increase Sanctions on the country of Iran!" Trump said in a tweet.

The United States already enforces widespread sanctions that have crippled Iran's economy, including attempting to shut down its major oil export industry.

Meanwhile, Iran's foreign minister Javad Zarif reacting to the announcement said, United States' newly announced sanctions against Iran showed it was aiming at civilians.

President Donald Trump's move was an "admission that (the) US is DELIBERATELY targeting ordinary citizens," Zarif wrote on Twitter, adding the measures were "illegal" and "inhuman".

Trump's comments come after weekend drone strikes on two major oil facilities in Saudi Arabia, which slashed the country's oil production by half and led both the kingdom and the United States to announce they may tap into their strategic reserves.

Watch: Saudi oil field attacks - Pompeo heads to Saudi as US blames Iran

Tehran-backed Huthi rebels in Yemen, where a Saudi-led coalition is bogged down in a five-year war, have claimed responsibility.

President Donald Trump has stepped up sanctions against Iran since last year when he exited a 2015 nuclear pact between Iran and six world powers and reimposed sanctions that were lifted under the deal in return for Iran curbing its nuclear program.

In response, Iran has gradually scaled back its commitments to limit uranium enrichment activity under the pact and plans to further breach it if European signatories fail to keep their promises to shield Iran's economy from US penalties.