WASHINGTON (Reuters) - U.S. President Joe Biden's approval ratings ticked up slightly in the last month, according to a poll conducted by Reuters/Ipsos, as more Americans named extremism and threats to democracy as their top worry ahead of the Nov. 5 election.

Two-fifths of Americans surveyed said they approved of Biden's performance, while 56% said they disapproved. That was a slight increase from last month's poll, which showed that 37% of respondents approved of Biden, close to the lowest level of his presidency.

The online poll was conducted March 22-24, after Biden's annual State of the Union address to Congress, where he delivered an energetic speech challenging Republicans that was intended to tamp down concerns about his age and vigor.

Biden, 81, is seeking a second term in office, where he is expected to face off against former President Donald Trump, 77, in the election.

A slightly larger number of respondents also expressed concerns over political extremism or threats to democracy, with 23% of respondents saying that was their top concern, up from 21% last month.

More than a third of Democrats - 36% - said that was their top worry, while 11% of Republicans and a quarter of independent voters said the same.

Trump has claimed, without evidence, that the 2020 election was stolen from him, including in a fiery speech shortly before hundreds of his supporters stormed the U.S. Capitol in 2021. Five people died.

Trump faces several legal challenges, including some tied to his role in attempting to overturn the results of the 2020 election.

On the campaign trail, Trump has said he would release people imprisoned for their role in the Jan. 6 attack and has referred to them as "hostages." He has also made a series of racist and inflammatory statements in his latest run for office.

Other top issues for voters were the economy, which 19% of respondents said was the most important problem for the country, and immigration, with 17% of respondents citing it as the top issue.

While 32% of Republican voters said immigration was their top concern, that was a decrease from last month's poll, which showed 38% of Republicans saw it as the top issue for the country.

Voters largely disapproved of the country's institutions.

Most people surveyed had unfavorable opinions of the House of Representatives (65%), the Senate (60%) and the Supreme Court (56%).

The Federal Reserve was the only institution that a majority favored, with 53% of poll respondents saying they had a favorable view.

The U.S. central bank has raised interest rates since March 2022 in a bid to lower inflation, but has kept rates steady since July and is expected to cut rates later this year.

The Reuters/Ipsos poll gathered responses online from 1,021 adults, using a nationally representative sample, with a margin of error of about 3 percentage points.