SAN FRANCISCO－Oregon State Governor Kate Brown said on Thursday that she would defy US President Donald Trump's plan to send National Guard troops to the US-Mexican border.

"I do not want our Oregon National Guardsmen and women to be used as political pawns," Brown told local media on Thursday.

Oregon TV station KATU2 reported that Trump "has not asked for National Guardsmen and women from Oregon, but she's promising to say 'no' if he does".

Trump signed a memorandum on Wednesday to deploy the National Guard to the southwest border, after days of calling for more border security.

The defense secretary "shall request use of National Guard personnel" to secure the border and the homeland security secretary will work with him to train and direct the troops in that mission, he said in the memo.

"The security of the United States is imperiled by a drastic surge of illegal activity on the southern border," Trump said.

Brown criticized the president for his poor handling of state affairs, saying, "This administration is governing via chaos and incompetence. It must stop."

"This is just something that the president reeled off to distract from the problems he's having in Washington, DC," she added.

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

According to US federal laws, the military are prohibited from being used for law enforcement. Troops can however perform support roles such as 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.