U.S. border authorities apprehended some 54,000 migrants illegally crossing the U.S.-Mexico border in October, according to preliminary figures obtained by Reuters, showing a marginal rise from September but continuing the broader downward trend since June when new restrictions were imposed under President Joe Biden.

Vice President Kamala Harris, the Democratic presidential candidate, has called for even tougher border restrictions in the face of criticism by Republican candidate Donald Trump over illegal immigration as the two compete in a tight race.

Immigration is a top issue for voters heading into Tuesday's election, particularly among Republicans, and Trump has intensified his language.

The roughly 54,000 migrant arrests from October 1 through October 30 were far less than the U.S. Border Patrol's monthly arrest average of 160,000 through the first eight months of fiscal year 2024, before the Biden restrictions were imposed. The preliminary data reviewed by Reuters did not include the final day of October.

In fiscal year 2023, border agents apprehended an average of 170,000 migrants per month.

In fiscal year 2019, before the pandemic and during Trump's presidency, the monthly average was about 71,000.

"We feel very confident in the strategy that we're employing to manage this," a senior U.S. Customs and Border Protection official said, requesting anonymity to discuss unpublished statistics. The official said the reduced crossings had allowed more agents to move to the field and target trafficking of people and drugs.

Biden's restrictions blocked most people crossing illegally from claiming asylum. At the same time, Mexico stepped up its immigration enforcement following U.S. pressure.

Trump cracked down on both legal and illegal immigration during his 2017-2021 presidency and has promised historic levels of deportations if reelected. Harris blames Trump for helping kill bipartisan legislation earlier this year that aimed to increase border security.

The Biden administration has also launched programs that have allowed hundreds of thousands of migrants to enter legally through emergency "parole," which Biden officials say has reduced illegal crossings. Republicans argue the Biden programs exceed the bounds of the law and serve as a workaround to allow migrants to enter the U.S.