Customs and Border Protection (CBP) on Friday said it had seen a "substantial increase" in fentanyl seizures at the southern border in January, just as it confirmed that there were 153,941 migrant encounters last month.

CBP’s monthly operational update confirmed Fox News’ reporting on Wednesday that there had been 153,941 encounters in what is typically a slow month for border crossers. The number is nearly double the 78,414 migrant encounters in Jan 2021, and more than quadruple the 36,585 in Jan 2020. 

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Of those encountered last month, 73% were single adults, and 51% of the total number of migrants were expelled via Title 42 public health protections put in place by the Trump administration and continued to an extent by the Biden administration. Of those, 62% of single adults were expelled under Title 42 and 26% of family units were returned.

There were 48,945 lbs of drugs seized at the southern border in January, which is down from 59,793 lbs encountered a year prior. However, fentanyl seizures were up, with 839 lbs seized in January, compared to 682 lbs in FY 2021 and 139 in FY 2020.

Fentanyl, an opioid for pain treatment, is between 50 and 100 times more potent than morphine. In Fiscal Year 2021, CBP seized 10,586 pounds of the deadly drug at the southern border, which can be fatal in extremely small amounts. That is up from 4,558 pounds seized in FY 2020 and 2,633 pounds seized in FY 2019. So far in FY 2022, agents have seized 3,289 lbs.

In its statement, CBP noted that compared to December, the border numbers had dropped 14% and drug seizures by 1%, but that fentanyl seizures were up 57%.

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"CBP’s January Monthly Operational Update shows migratory flows decreased in January, with CBP personnel encountering 14 percent fewer individuals along the Southwest border than December. Most encounters in January were of single adults and a majority were expelled under Title 42," said CBP Commissioner Chris Magnus in a statement. 

"Overall illegal narcotic seizures decreased, though there was a substantial increase of fentanyl interdictions. CBP continues to take important steps to improve our ability to interdict narcotics and keep dangerous drugs off our streets," he said."

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The numbers of migrants at the border are likely to be of continued concern to CBP, given that January is typically a slow month for migrant crossings and comes as FY 2022's numbers continues to outpace FY 2021.

Between October 2020 and January FY 2021, there were 296,720 migrant encounters. This fiscal year, between October and January, there have been 672,848.

Fox News' Bill Melugin contributed to this report.