WASHINGTON (REUTERS) - A nationwide wave of arrests of immigrants facing deportation will commence this weekend, US President Donald Trump said on Friday (July 12), confirming that the plan, intended to discourage a surge of Central American migrants, was on track after a delay.

The operation, to be carried out in 10 cities, is expected to target families that have recently been ordered deported by an immigration court but have not yet left the country.

Trump previously announced the operation on Twitter last month and then postponed it.

It is unusual for the government to announce deportation operations ahead of time.

"People are coming into this country illegally, we are taking them out legally," Trump told reporters on Friday, calling it a "major operation" that would mainly focus on removing criminals.

In a typical week, US Immigration and Customs Enforcement (ICE) arrests thousands of immigrants who are staying in the country illegally, according to government data.

Most of those arrests are made without any special publicity.

Immigrant advocates have said advance word of the weekend raids could help some of those targeted to evade arrest.

But the president, speaking to reporters at the White House on Friday, said he was not concerned that the advance notice could help targeted immigrants evade arrest.

"If the word gets out, it gets out," he said.

Democratic lawmakers, among others, have also sought to inform immigrants of their rights, telling them not to open their door for ICE unless agents present a court-issued warrant, and not to say or sign anything before speaking with a lawyer.

Trump, who has made cracking down on illegal immigration a centrepiece of his administration, is trying to deal with a surge of mostly Central American families crossing the US-Mexico border.

Many families are approaching border officials to seek asylum.

The latest planned arrests would follow widespread criticism of the crowded, unsanitary conditions in which immigrants are being detained along the southwestern border and concerns about children being separated from adults by border officials.

In a hearing on the subject on Friday at the US House of Representatives, some Democrats said they feared the forthcoming arrests could result in more immigrant children being separated from their families.

Mr Elijah Cummings, the chairman of the House Oversight and Reform Committee, asked a federal watchdog about its recently issued report saying detention conditions were below standards.

Ms Jennifer Costello, the acting inspector general for the Department of Homeland Security, told the congressional hearing that the government was falling short in terms of "crowding, the prolonged detention, some of the hygiene that the children are supposed to have."

Ms Costello said it would be "impossible" to meet required standards under "the conditions that we saw there."

"It's shocking," she said.

Trump sent Vice-President Mike Pence to visit some of the criticised detention facilities in McAllen, Texas, on Friday along with journalists, who have generally been denied access to detained immigrants.

Pence visited one overcrowded and foul-smelling facility where almost 400 men are detained behind metal fences, some sleeping on concrete, after being accused of crossing the US border illegally.

The Trump administration has increased pressure on the governments of Mexico and several Central American countries to stem the flow of migrants reaching the US border.

Trump is to meet with Guatemalan President Jimmy Morales at the White House on Monday for talks on immigration and security.

Morales may sign an agreement with Trump declaring Guatemala a safe destination for asylum seekers, which could prevent many from applying in the United States, according to officials in both governments.

Alongside these international efforts, Trump has sought to deter border crossings with highly publicised crack-downs in the United States.

ICE will target families whose immigration cases were handled through an expedited court process that began in 2018, the acting ICE director said last month.

The agency has notified about 2,000 of those people that they face deportation because they failed to appear in court, acting ICE Director Mark Morgan said last month.

ICE has declined to discuss the weekend's operation, including whether those families are among those being targeted.

Mayors of a number of cities expected to be targeted have said they would not cooperate with ICE officials on deportations.

Democratic lawmakers, among others, have circulated information advising immigrants of their rights, telling people they do not have to open their door for ICE unless the agents present a court-issued warrant.