LONDON (Reuters) -The United States and Britain are expected to announce a deal to lower tariffs on some goods on Thursday, the first such agreement since U.S. President Donald Trump imposed levies on countries around the world.

Trump posted on Truth Social that he would hold an Oval Office news conference at 10 a.m. EDT (1400 GMT) on Thursday about a "major trade deal with representatives of a big, and highly respected, country."

A British government spokesperson said Prime Minister Keir Starmer would give an update on U.S.-UK trade talks later on Thursday. Two British people familiar with the situation said the outline of an agreement would be announced.

"The United States is an indispensable ally for both our economic and national security," a Downing Street spokesperson said. "Talks on a deal between our countries have been continuing at pace and the Prime Minister will update later today."

A British official had said on Tuesday that the two sides were working to agree lower tariff quotas - a tranche of exports subject to lower duties - on steel and autos, two sectors that were hit by 25% U.S. levies.

In return, Britain is likely to agree to lower its own tariffs on U.S. cars and cut a digital sales tax that affects U.S. tech groups. It has refused to lower its food standards in order to give U.S. producers greater market access.

The status of a 10% "baseline" tariff imposed by Trump on most countries including Britain was unclear.

Despite the potentially narrow nature of any deal, it will be politically significant for both countries.

Investors have been looking to see whether Trump can de-escalate his trade war after the launch of global tariffs risked reigniting inflation and slowing economic growth.

For Britain, the government is trying to reduce the worst of the damage from Trump's tariffs without damaging its efforts to reset its trade relationship with the European Union. It also agreed a new trade deal with India earlier this week.

Trump's trade war has shaken up financial markets and raised fears of a recession, with central bankers and business executives wrestling with often chaotic policymaking that is hitting world supply chains and a whole host of industries.

The International Monetary Fund last month slashed its growth forecasts for the United States, China and most countries, citing the impact of U.S. tariffs and warning that rising trade tensions would further slow growth.

U.S. and Chinese officials are also preparing to hold talks in Switzerland on Saturday, which could mark the first step in resolving a potentially damaging trade war between the world's top two economies.

Trump's top officials have engaged in a flurry of meetings with trading partners since the president on April 2 imposed the broad 10% tariff, along with higher "reciprocal" tariff rates for many trading partners, though those rates were later suspended for 90 days.

Britain was not among the countries hit with additional tariffs, because it imports more from the U.S. than it exports there.