Homeland Security Secretary Alejandro Mayorkas defended the Biden administration’s border policy Thursday as he announced another monthly rise in migrant encounters amid concerns over COVID-19 spread.

At a news conference in Brownsville, Texas, Mayorkas said border agents logged more than 210,000 encounters with migrants along the U.S.-Mexico border in July, a 13 percent increase from June.

Because many encounters involve migrants who make repeated attempts to cross, Mayorkas said the number of unique individuals encountered by border agents in July was lower: just over 154,000, compared to roughly 124,000 unique individuals in June.

The number of children crossing the border without their parents is also on the rise. Border agents encountered 18,962 unaccompanied children in July, a 24 percent increase from the prior month.

Meanwhile, Customs and Border Protection — whose short-term detention facilities are not designed for children — had an average of more than 1,300 kids in its custody each day, up from an average of 794 per day in June.

“The situation at the border is one of the toughest challenges we face,” Mayorkas said. “It is complicated, changing, and involves vulnerable people at a time of a global pandemic.”

Mayorkas added that border agents have encountered more than 845,000 unique migrants at the border so far in fiscal 2021, compared with just under 800,000 during the same period in fiscal 2019.

The Biden administration has faced increasing criticism in recent weeks that migration at the U.S.-Mexico border could be contributing to COVID-19 spread as the more transmissible delta variant surges.

Border communities, meanwhile, say migrant arrivals have strained their resources. While in Texas, Mayorkas met with Democratic Rep. Henry Cuellar and other local leaders who advocated for a moratorium to temporarily stop asylum-seeking migrants from entering the country.

“We want to humanely, safely take care of all people that are here, but there are times that we need all the capacity that we have in order to serve our communities,” Hidalgo County Judge Richard Cortez said at a separate news conference Thursday.

Mayorkas insisted the Biden administration was working to reduce migration at the U.S.-Mexico border, including through efforts to address the root causes of migration in Central America and expand alternate pathways for asylum-seekers. Most single adults and some families continue to be expelled at the border under a public health directive known as Title 42 implemented during the Trump administration.

“We are prepared to do more as the situation warrants,” Mayorkas said. “It is critical that intending migrants understand clearly that they will be turned back if they enter the United States illegally and do not have a basis for relief under our laws.”

Earlier on Thursday, former Department of Homeland Security leaders under the Trump administration slammed the Biden administration’s handling of high migration levels at the southwest border at a virtual event hosted by the Heritage Foundation.

Chad Wolf, who served as acting Homeland Security secretary under President Donald Trump, told reporters the Biden administration “doesn’t have a strategy to effectively deal with this.”

And while the Biden administration has continued rapidly “expelling” most single adults under Title 42 and revived fast-tracked deportations for families, Wolf claimed the administration has merely paid “lip service” to those authorities.

“In all cases, they are not utilizing each of these authorities to the maximum extent that they could,” Wolf said. “Instead, it’s almost as though they give it lip service in not doing everything they could under each of these authorities to make sure that the border is safe and secure.”