WASHINGTON, April 6 (Xinhua) -- U.S. President Donald Trump said Thursday that he wants to send between 2,000 and 4,000 National Guard members to the U.S.-Mexico border.

"We're looking at a combination of from 2,000 to 4,000. We're moving that along." Trump told reporters. "And we'll probably keep them, or a large portion of them, until such time as we get the wall."

The remarks followed a proclamation he signed Wednesday, directing the deployment of the National Guard to the border with Mexico, citing a crisis situation.

"The lawlessness that continues at our southern border is fundamentally incompatible with the safety, security, and sovereignty of the American people," Trump said in a memo.

The president has been publicly fuming over the immigration policy and border security situation, due to what he calls "weak" border laws.

He has repeatedly called out Mexico over border security and stressed the need for a wall on the southern border.

In response, Mexican President Enrique Pena Nieto urged the U.S. president not to take out his frustration over domestic policy matters on Mexico.

"If your recent statements derive from frustration over domestic policy issues ... address them, not Mexicans. We will not allow negative rhetoric to define our actions," Pena Nieto tweeted.

During a White House news briefing on Wednesday, U.S. Homeland Security Secretary Kirstjen Nielsen said the National Guard would support U.S. Custom and Border Protection but would not be involved in enforcement.

According to U.S. federal laws, the military are prohibited from being used for law enforcement. Troops can however play support roles like in training, construction and intelligence gathering.

Though sending the National Guard to the border is not unprecedented, similar moves by Trump's predecessors were criticized for their high cost and limited effectiveness.

Trump has also proposed using military funding to build the wall, after the newly-signed 1.3-trillion-U.S.-dollar spending bill allocated only 1.6 billion dollars for border security measures, far short of what the administration sought.