Donald Trump has been tougher on “tearing” immigrant children from their families than he has on Vladimir Putin, veteran senator Bernie Sanders has claimed.

The former presidential candidate took aim at the US leader for failing to stand up to his Russian counterpart, whose country interfered with the 2016 election, according to American intelligence services.

The Vermont senator also criticised the president for “tearing” children and their families apart as part of his “zero tolerance” border policy.

“We say to Trump, instead of showing us your strength by tearing children from their families, where was your strength in standing up to Putin and Russia for undermining American democracy,” he told crowds at a large rally. "How courageous he is to tear children from their families, how cowardly he is to stand up to people who are trying to undermine not only American democracy but other aspects of our lives.

He added: “We have a president that’s so tough when he’s terrorising little children. When he was up against Vladimir Putin, he wasn’t so tough.”

Mr Trump faced criticism from both sides of the political divide following a joint press conference with Vladimir Putin earlier this week.

The American president appeared to side with Mr Putin's denial about Russian election meddling over his own intelligence community's assessment.

Undocumented immigration across the US-Mexico border Show all 14 1 /14 Undocumented immigration across the US-Mexico border Undocumented immigration across the US-Mexico border Immigrant children, many of whom are separated form their parents, are housed in Texas' tent city Reuters Undocumented immigration across the US-Mexico border A two-year-old Honduran asylum seeker cries as her mother is searched and detained near the US-Mexico border Getty Undocumented immigration across the US-Mexico border Undocumented migrants ride on the top of a freight train referred to as the beast, or La Bestia Getty Undocumented immigration across the US-Mexico border A cage inside a US Customs and Border Protection detention facility in Texas Reuters Undocumented immigration across the US-Mexico border US Border Patrol Academy All new agents must complete a months-long training course at the New Mexico facility before assuming their posts at Border Patrol stations, mostly along the US-Mexico border Getty Undocumented immigration across the US-Mexico border US-Mexico border fence A group of young men walk along the Mexican side of the US-Mexico border fence in a remote area of the Sonoran Desert Getty Undocumented immigration across the US-Mexico border US-Mexico border fence in the US Man looks through US-Mexico border fence into the US in Tijuana, Mexico Getty Undocumented immigration across the US-Mexico border US-Mexico border fence US Border Patrol agent Sal De Leon stands near a section of the US-Mexico border fence while stopping on patrol on in La Joya, Texas Getty Undocumented immigration across the US-Mexico border US Border Patrol Academy US Border Patrol instructor yells at trainees after their initial arrival to the academy Getty Undocumented immigration across the US-Mexico border Memorial service in Guatemala Families attend a memorial service for two boys who were kidnapped and killed in San Juan Sacatepequez, Guatemala. Crime drives emigration from Guatemala to the United States, as families seek refuge from the danger Getty Undocumented immigration across the US-Mexico border Arrests on the border Undocumented immigrants comfort each other after being caught by Border Patrol agents near the US-Mexico border Getty Undocumented immigration across the US-Mexico border Detention holding facility A boy from Honduras watches a movie at a detention facility run by the US Border Patrol Getty Undocumented immigration across the US-Mexico border Mexican farm workers Mexican migrant workers harvest organic parsley at Grant Family Farms in Wellington, Colorado Getty Undocumented immigration across the US-Mexico border Mexican family in Arizona A Mexican immigrant family sits in the living room of their rented home in Tuscon, Arizona. The family that Arizona's new tough immigrant law had created a climate of fear in the immigrant community. Getty

While discussing whether he thought Russia was behind hacks against the election, Mr Trump said: ”I don’t see any reason why it would be.“

He later backtracked on the remarks, saying: “I accept our intelligence community's conclusion that Russia's meddling in the 2016 election took place.”

But he added: “Could be other people also. A lot of people out there.”

The separation of children from their parents because of Mr Trump’s “zero tolerance” illegal immigration policy at the US-Mexico border has sparked a nationwide backlash.

The policy means all cases of adult illegal entry are sent for criminal prosecution, while their children are sent to different care facilities across the US.

Images emerged of youngsters in tent camps and holding facilities made up of cages.