WASHINGTON, July 29 (Xinhua) -- U.S. President Donald Trump on Sunday threatened to shut down the U.S. government if the Democratic Party does not cooperate on border security issues.

"I would be willing to 'shut down' government if the Democrats do not give us the votes for Border Security, which includes the Wall! Must get rid of Lottery, Catch & Release etc. and finally go to system of Immigration based on MERIT! We need great people coming into our Country!" Trump said on Twitter.

The threat came on top of another fiery tweet posted earlier Sunday, which said "please understand, there are consequences when people cross our Border illegally, whether they have children or not - and many are just using children for their own sinister purposes. Congress must act on fixing the DUMBEST & WORST immigration laws anywhere in the world! Vote 'R,'" referring to Republicans.

The tweets were in response to attacks on the U.S. government's family separation policy, which saw thousands of minors separated from their parents who entered the United States illegally.

The controversy that ensued the family separation policy caused many Republican lawmakers to distance themselves from Trump's tough immigration agenda, and has stalled legislative progress in Congress for comprehensive immigration reform, which had been a major promise for his supporters since his 2016 campaign.

However, Trump's menacing tweets were rebuffed even by his own party members, who said shutting down the government will not be helpful.

Congressman Steve Stivers, a Republican from Ohio, downplayed the possibility of a shutdown in a TV interview on Sunday, saying: "I think we're going to make sure we keep the government open."

The U.S. federal government has been occasionally shut down in recent years, mostly when Congress failed to reach a spending bill due to political fights.