Washington DC - President Donald Trump signed pardons Thursday for 23 anti-abortion protesters whom the White House said were prosecuted under his predecessor Joe Biden's administration.

"They should not have been prosecuted. Many of them are elderly people," Trump told reporters in the Oval Office the day before a major anti-abortion march in Washington.

"This is a great honor to sign this."

An aide at the ceremony said the pardoned people were "peaceful pro-life protesters," but the White House did not immediately release more details on them.

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US media said the protesters were convicted of blocking access to abortion clinics.

Republican Trump is reportedly due to address the March for Life in Washington on Friday by video, while Vice President JD Vance is set to appear in person.

Trump has recently kept his position on the politically explosive issue of abortion deliberately vague.

While the Christian right has called for federal restrictions on the practice, Trump has said he wants to leave the issue to individual states to decide.

But he has repeatedly claimed credit for the 2022 ruling by the Supreme Court – conservative-dominated thanks to justices appointed during his first term – that overturned the nationwide federal right to abortion.

Since the Supreme Court ruling, at least 20 states have brought in full or partial restrictions on abortion.

Trump has reached out to his base with a series of pardons since starting his second presidential term on Monday.

Within hours of his inauguration, he pardoned some 1,500 people accused of involvement in the January 6, 2021, attack on the US Capitol by supporters trying to overturn his election loss to Biden.

Trump then on Wednesday pardoned two police officers who were convicted over the death of a 20-year-old Black man in a car chase in Washington in 2020.