ERBIL, Kurdistan Region of Iraq - US President Donald Trump on Wednesday said that they will "hit Iran hard today" after the downing of a US Apache helicopter led to both sides trading strikes the day prior, threatening a peace process that appears to be struggling amid renewed skirmishes.

Speaker to reporters in the Oval Office, Trump said, "I have been working with Iran for a number of months, and they should sign the deal. It's a good deal," adding that Pakistani mediators are continuing to work on reaching an accord.

The US and Iran exchanged fire early Wednesday after the Iranian army carried out missile attacks against targets in response to American "self-defense" strikes, which US President Donald Trump said were in response to Iran shooting down an Apache helicopter over the Strait of Hormuz. 

Iran responded by striking US bases across the Middle East, with state media saying at least 21 targets were struck in Jordan, Bahrain and Kuwait. 

"We were really close to a deal, but they keep tapping us along, they keep playing us for suckers," the president said.

"We'll see what happens - we hit them hard yesterday, we're going to hit them hard again today, in case you miss it, in case you don't turn on your television set."

The president also appeared to claim that the US has been covertly seizing Iranian oil as part of its naval blockade of Iranian ports, telling the audience that "we have been taking out millions of barrels of oil. Nobody knows it. You know who doesn't know about it? Iran, until right now."

Earlier in the day, Trump had lamented that Tehran was taking too long to reach a deal, coming after Iranian strikes on Israel, in retaliation for the latter's continued bombardment of Lebanon, threw a spanner in the works of the negotiating process.

Despite the set back, prospects were still relatively positive, though the recent flare up has threatened a broader return to conflict.