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NEW YORK, Feb 23 (Reuters) - The dollar fell on Monday as traders assessed trade policies after the Supreme Court on Friday struck down tariffs previously imposed by President Donald Trump. Traders also watched escalating tensions with Iran, which is in talks with the United States over a nuclear agreement.

In a 6-3 ruling drafted by conservative Chief Justice John Roberts, the justices upheld a lower court's decision that Trump exceeded his authority by using the 1977 emergency law.

Trump responded by saying he would look for alternative ways to impose tariffs.

"The biggest problem is the current uncertainty," said Sarah Ying, head of foreign exchange strategy at CIBC Capital Markets in Toronto. "How the market will deal with this is also somewhat unclear."

The euro rose 0.23 percent to $1.1807, and the Japanese yen gained 0.43 percent against the US dollar to 154.41 yen.

The British pound rose 0.27 percent to $1.3519.

Trump said on Saturday that he would raise temporary tariffs to 15 percent from 10 percent on U.S. imports from all countries, the maximum allowed by law. The new tariffs are based on an untested law known as Section 122, which allows for tariffs of up to 15 percent but requires congressional approval to extend them after 150 days.

He added that he would use the 150-day period to work on imposing other tariffs "legally permissible." In a social media post today, Trump also hinted at the possibility of using his powers to pressure other countries.

Ying said, "There is a lot of debate in the market about whether imposing more tariffs will have a negative or positive impact on the dollar."

She added, "For example, stricter tariffs could increase inflation and reduce the likelihood of the Federal Reserve (the US central bank) making further interest rate cuts, which in turn would lead to a rise in the value of the dollar. On the other hand, increased uncertainty increases the risk of a decline in the dollar, which would have a negative impact on the currency."

The European Parliament decided today to postpone the vote on the trade agreement between the European Union and the United States because of the new tariffs.

US Treasury Secretary Scott Bessent expressed his belief on Friday that all countries would abide by the trade agreements concluded with the Trump administration during the past year.

It is not yet clear whether companies that paid customs duties will be able to get a refund.