Copper prices slipped on Tuesday after three sessions of gains on uncertainty about tariffs being imposed by U.S. President Donald Trump and the impact on global growth.

Three-month copper on the London Metal Exchange (LME) dropped 0.5% to $9,145 a metric ton in official open-outcry trading. In the previous session, the contract hit its highest level since April 4.

"This is still a very stressful market where we're moving from one headline to the next," said Ole Hansen, head of commodity strategy at Saxo Bank in Copenhagen.

The U.S. removed smartphones and other electronics from its tariffs on China over the weekend and Trump on Monday suggested he might grant exemptions on auto-related levies already in place.

"The market is perhaps starting to call Trump's bluff. He's not really going to carry out all of them because it's probably starting to dawn on him the negative impact on the U.S. economy in the short term."

After Trump imposed tariffs on aluminium and steel and ordered a probe into possible copper duties, traders have been trying to price in the impact on the copper market.

U.S. Comex copper futures dropped 1.3% to $4.56 a lb, bringing the premium of Comex over LME to $955 a ton, up from $572 last Thursday.

The most-traded copper contract on the Shanghai Futures Exchange (SHFE) added 0.2% to 75,970 yuan ($10,394.03) per ton.

Helping support the market was declining copper inventories on SHFE , which have shed 32% since February 24.

Also boosting sentiment was expectations that top metals consumer China will launch more stimulus measures to bolster consumption and cushion the economic impact of an escalating China-U.S. trade war.

LME aluminium was flat in official activity at $2,374 a ton, zinc lost 0.3% to $2,628, tin fell 0.7% to $31,075 while lead gained 0.7% to $1,929 and nickel advanced 1.8% to $15,575. ($1 = 7.3090 Chinese yuan)

(Reporting by Eric Onstad, editing by David Evans, Kirsten Donovan)