Washington, Jul 28 (IANS): In an unexpected endorsement, former US president Barack Obama has shared on his Twitter handle a letter by former members of his administration that rebuked racism in American politics and called out President Donald Trump for his racist comments made against four Congresswomen of colour.

The letter, co-signed by 149 African Americans, appeared as an op-ed in The Washington Post on Friday.

Sharing it on Twitter late on Saturday, Obama wrote: "I've always been proud of what this team accomplished during my administration. But more than what we did, I'm proud of how they're continuing to fight for an America that's better."

In the op-ed titled, "We are African Americans, we are patriots, and we refuse to sit idly by", the former Obama administration officials vowed to stand up against the "racism, sexism, homophobia and xenophobia... wielded by the President (Trump)".

"There is truly nothing more un-American than calling on fellow citizens to leave our country -- by citing their immigrant roots, or ancestry, or their unwillingness to sit in quiet obedience while democracy is being undermined," they wrote.

The letter was written as a reaction to Trump's tweet that the four minority lawmakers should "go back" to the places they came from.

Trump reportedly post the tweet after a crowd of his supporters at a campaign rally chanted "Send her back!" at the mention of US Representative Ilhan Abdullahi Omar, a Somali refugee who became a US citizen in 2000.