A top border official said Wednesday that of the tens of thousands of unaccompanied children from El Salvador, Guatemala and Honduras detained by U.S. authorities this year, something on the order of 3 percent have been deported so far.

Thomas Winkowski, deputy assistant secretary for U.S. Immigration and Customs Enforcement, offered that estimate at a Senate Homeland Security and Governmental Affairs hearing Wednesday morning.

Darlene Mosser, of Ventura, is among many crowd members expressing their opinions through signs, about immigrant children who are being temporarily housed at a naval base in Port Hueneme, Calif., Tuesday, July 8, 2014. Most of the 57,000 children detained so far have not been deported. (AP Photo/Ventura County Star, Karen Quincy Loberg)

Winkowski was pressed by Sen. Ron Johnson (R-Wis.), who asked how many children who crossed the border this year have been returned so far. Winkowski estimated, “thirteen, fifteen hundred.”

Winkowski later clarified that this estimate refers only to children from the three Central American countries, and not children from Mexico who can often be deported much more quickly.

Officials didn’t have updated figures for how many Central American children have been apprehended so far. But as of mid-June, U.S. Customs and Border Protection reported that 39,000 of these children had been apprehended so far.

That number has likely grown by a few thousand, as a CBP official said today the total number of children has increased by 5,000 over the last few weeks, to 57,000. That means at best, a little more than 3 percent of these children have been deported so far.

Both Republicans and Democrats have noted that deportation proceedings are much slower for Central American children than they are for Mexican children. The Obama administration said last week that it wanted to change the law to speed up this process, but officials have since dropped that demand for a change to the law.