Washington, United States (AFP)-US President Donald Trump reignited his trade war by threatening more than a dozen countries with higher tariffs Monday — but then said he may be flexible on his new August deadline to reach deals.

Trump sent letters to trading partners including key US allies Japan and South Korea, announcing that duties he had suspended in April would snap back even more steeply in three weeks.

Tokyo and Seoul would be hit with 25 percent tariffs on their goods, he wrote. Countries including Indonesia, Bangladesh, Thailand, South Africa and Malaysia were slapped with duties ranging from 25 percent to 40 percent.

But in a move that will cause fresh uncertainty in a global economy already unsettled by his tariffs, the 79-year-old once again left the countries room to negotiate a deal.

“I would say firm, but not 100 percent firm,” Trump told reporters at a dinner with visiting Israeli Prime Minister Benjamin Netanyahu when asked if August 1 deadline was firm.

Pressed on whether the letters were his final offer, Trump replied: “I would say final — but if they call with a different offer, and I like it, then we’ll do it.”

The US president had unveiled sweeping tariffs on imports on what he called “Liberation Day” on April 2, including a baseline 10 percent tariff on all countries.

But he quickly suspended all tariffs above 10 percent for 90 days following turmoil in the markets.

They were due to kick back in on Wednesday and Trump sent the letters in advance of that deadline.

Trump’s near-identically worded letters to Japanese and South Korean leaders said he would impose 25 percent tariffs as their trading relationships with Washington were “unfortunately, far from Reciprocal.”

He warned of further escalation if there was retaliation against the levies.

But Trump on Monday also signed an order formally extending the Wednesday deadline, postponing it to August 1.