Media playback is unsupported on your device Media caption Loudspeakers and heckling as activists protest against family separations in Washington DC

Protesters have barracked a Trump administration official as she dined at a Mexican restaurant in Washington DC.

The activists heckled Homeland Security Secretary Kirstjen Nielsen at the eatery near the White House.

The Trump administration is facing international pressure to drop its new policy of taking migrant children from their parents.

They include babies and toddlers sent to three "tender age" shelters, the Associated Press news agency reports.

The Metro DC Democratic Socialists of America claimed responsibility for Tuesday evening's protest against the homeland security secretary.

Her security detail kept the demonstrators from approaching too near her table at the back of the restaurant.

The activists shouted: "How do you sleep at night?"

"If kids don't eat in peace, you don't eat in peace."

"Do you hear the babies crying?"

"Aren't you a mother, too?"

Ms Nielsen later tweeted: "I will work tirelessly until our broken immigration system is fixed, our borders are secure and families can stay together."

President Donald Trump has said the homeland security secretary "did a fabulous job" defending the controversial policy at a news conference this week.

Meanwhile, a former Trump campaign manager made fun of a story about a 10-year-old girl with Down's syndrome who was reportedly separated from her mother after crossing the border illegally.

Appearing on Tuesday on Fox News, Corey Lewandowski sarcastically said "womp, womp", as a Democratic party aide said the girl had been "taken from her mother and put in a cage".

The Democratic adviser, Zac Petkanas, shouted repeatedly: "How dare you!"

The unconfirmed report of the so-called tender age shelters for babies and toddlers drove an MSNBC news anchor on Tuesday night to almost break down in tears.

When she first received the breaking news report from the Associated Press, Rachel Maddow paused.

Media playback is unsupported on your device Media caption The sound of migrant children separated from parents

"This is incredible. Trump administration officials have been sending babies and other young children..." she trailed off, before covering her mouth and saying she was unable to continue.

On Wednesday, Republican Speaker of the House Paul Ryan said lawmakers plan to vote on Thursday on an immigration bill that could end the practice of family separations.

In a USA Today op-ed, Attorney General Jeff Sessions wrote that the migrant children "get better care than a lot of American kids do".

Tom Homan, the acting director of Immigrations and Customs Enforcement, told CNN: "If you want to blame someone for separating families, blame the parents who choose to break the law."

Media playback is unsupported on your device Media caption Theresa May: US child detention "disturbing" and "wrong"

On Tuesday, a group of US lawmakers were denied entry to a detention centre for migrant children in Homestead, Florida. Nearly 1,000 children are being held there, according to homeland security officials.

"This is an absolute outrage," said Congresswoman Debbie Wasserman Schultz, standing outside the facility.

This is not the first time lawmakers have been turned away from visiting migrant shelters, which now contain nearly 12,000 children, according to government figures.

Media playback is unsupported on your device Media caption Zero-tolerance: The US policy dividing families and opinion

There is anecdotal evidence that the Trump administration's "zero tolerance" crackdown, launched last month, may be achieving its objective of deterring migrants crossing the border illegally.

Salvadoran postman Cen Epigmenio told Reuters news agency he hoped to cross the Mexican border into the US in the coming months.

But the 40-year-old said he and his wife have postponed their plans for fear of being separated from their two sons, Axel, nine, and Steven, three.

He said he was fleeing gang violence at home.

"As things stand today, it's difficult, because if you get caught, they take your kids away. I think I'm going to stay here, in Mexico, and establish myself."

Another Salvadoran migrant, Lucia Carmen Flores Sanchez, who is travelling overland with her eight-year-old daughter, told the New York Times a similar story.

Where are the children taken?

Holding cells: The children are first detained at Customs and Border Protection (CBP) facilities, where chain-link fenced enclosures are used, though the children can only be legally held there for three days.

Detention centres: The children are then moved into around 100 detention centres run through the Office of Refugee Resettlement (ORR), which is part of the Department of Health and Human Services. US officials recently showed reporters around a converted Walmart Supercenter in Texas which was housing migrant boys aged 10-17. They apparently had access to beds, classes and games.

Media playback is unsupported on your device Media caption Migrant boys detained in a former Walmart in Texas

"Tender age shelters": A CBP official said it is up to the discretion of border agents whether to detain "tender-aged" children, who are typically less than five years old. AP news agency reports that babies and toddlers are being taken to three "tender age shelters" in southern Texas.

Tent cities: US officials have set up a tent camp for migrant children in Tornillo, Texas, which a BBC reporter will visit on Wednesday.

Family members: Under law, the children are supposed to be released to stay with relatives or foster carers "without delay". But the ORR says this process takes "fewer than 57 days on average".

How are families reunited? Immigrations and Customs Enforcement (ICE) has set up a hotline for parents to call after they are released from custody. However, a former ICE director has said some family separations are "permanent".

More on child migrants crisis

Media playback is unsupported on your device Media caption The US teens training in border patrol