WASHINGTON: Almost 180,000 migrants were apprehended attempting to enter the United States from Mexico in December, official figures published Monday showed.

The additional 178,840 detentions in December bring the total number of apprehensions at the US southern border in 2021 to almost two million -- a record.

The Republican Party quickly accused Democratic President Joe Biden and his Vice President Kamala Harris of having created a "historic humanitarian crisis."

"On their watch, cartels and smugglers are thriving, border officials are overwhelmed, our communities are less safe," said Republican National Committee chairwoman Ronna McDaniel in a statement.

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Migrant arrivals to the United States declined markedly during the initial phase of the Covid-19 pandemic but began to pick up later in 2020, before surging since President Joe Biden took office in January last year.

His arrival in the White House, with a promise of a more humane approach towards migrants, led to an increase in flows of undocumented foreigners fleeing poverty and violence.

Figures over the summer demonstrated a deviation from seasonal trends.

Punishingly hot summer weather usually sees the number of migrants attempting to cross decrease but the US Department of Homeland Security said an "unprecedented" number of migrants -- around 200,000 -- were intercepted illegally crossing the US-Mexico border in July.

The arrivals pose a considerable human, logistical and financial challenge to the Democratic administration, particularly as it has pledged not to turn back unaccompanied minors.

Its efforts to overhaul the migration system have stalled in Congress, and the issue is expected to be a major issue in the midterm elections in November.