Washington, DC - Outgoing-president Joe Biden on Sunday said that President-elect Donald Trump's threats to end birthright citizenship in the US were "awful."

Trump has dropped increasingly strong hints that he aims to end birthright citizenship as part of a systematic attack on immigrants, with or without documentation.

Speaking to reporters on Sunday about the fourth anniversary of the January 6 Capitol riot, Biden responded by saying: "We are the most extensive multicultural nation in the world. It's the reason why we're so strong. It's the reason why we're who we are."

"The idea we're going to change a constitutional birthright – if you're born in the country ... you're not a citizen? What's going on?" he added.

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"It's awful, it's awful."

As early as 2018, Trump promised that birthright citizenship "will be ended one way or the other."

In an early-December interview, Trump reiterated his call to end the practice during a sit-down interview with NBC, taking aim at the 14th amendment and vowing to "get it changed."

Currently, if a non-US citizen gives birth while ion the sovereign US territory, the baby is automatically granted citizenship.

A change to such a law would be in breach of the US Constitution's 14th Amendment, which states that: "No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States."

In response, Trump has hinted at possibly pursuing a constitutional amendment.