WASHINGTON -  President Donald Trump on Friday signed an executive order aimed at limiting the "burden" of the Obamacare health law that the incoming US leader has vowed to repeal.

The Trump’s administration also announced its commitment to eliminate the Climate Action Plan, the centrepiece of former President Barack Obama’s climate legacy, according to a posting on the White House’s official website. “For too long, we’ve been held back by burdensome regulations on our energy industry,” the website said in a page titled “An America First Energy Plan.” “President Trump is committed to eliminating harmful and unnecessary policies such as the Climate Action Plan and the Waters of the US rule.”

It claimed that lifting these restrictions will “greatly help American workers, increasing wages by more than 30 billion US dollars over the next seven years.”

During the signing in the Oval Office, Trump's chief of staff Reince Priebus described the order as aimed at "minimizing the economic burden" of the 2010 Affordable Care Act, "pending repeal." Doing away with Barack Obama's signature domestic achievement is a top priority for Republicans, who control both chambers of Congress and, since Trump's inauguration Friday, the White House. In their view, Obamacare - which aimed to ensure healthcare for the millions of Americans who are neither covered by public insurance, nor by their employers - marked a costly drift toward socialized, European-style medical care.

Until lawmakers are able to repeal Obamacare, "it is imperative for the executive branch to... take all actions consistent with law to minimize the unwarranted economic and regulatory burdens of the Act, and prepare to afford the States more flexibility and control to create a more free and open healthcare market," the executive order said.

The order instructs the US health secretary and other departments and agencies to "exercise all authority and discretion available to them to waive, defer, grant exemptions from, or delay the implementation of any provision or requirement of the Act" that imposes a fiscal burden or other cost on a state, on consumers, on insurers or on a range of healthcare providers.  The president has said the law should be repealed and replaced "simultaneously," a stiff challenge given the complexity of America's vast health care system. Obamacare added more than 20 million people onto insurance rolls, lowering the percentage of Americans without coverage from 16 percent in 2010 to 8.9 percent last year.

US President Donald Trump plans to visit CIA headquarters on Saturday in what could be an effort to mend fences after he criticized spy agencies for their investigation into Russian hacking during the presidential election. White House spokesman Sean Spicer said on Twitter than more than 300 people would attend the event at the Central Intelligence Agency, based in Langley, Virginia. “Excited to thank the men and women of the intelligence community,” Spicer said.

Meanwhile, Israeli Prime Minister Benjamin Netanyahu said on Saturday he planned to discuss soon with US President Donald Trump how to “counter the threat” from Iran.

“I plan to speak soon with President Trump about how to counter the threat of Iranian regime which calls for Israel’s destruction,” Netanyahu said in a video message posted on his Facebook page.

Meanwhile, retired Marine general James Mattis was sworn in Friday as US defence secretary, praising intelligence agencies and calling for stronger ties with allies in a break from positions taken by President Donald Trump.

Mattis was confirmed by a 98-1 vote earlier Friday in the first action taken by US senators after Trump took the oath of office, and was sworn in by Vice President Mike Pence.

"Together with the intelligence community we are the sentinels and guardians of our nation," Mattis said in a statement to the Department of Defence - tipping his cap to the agencies that Trump has sharply criticized as they investigate claims of Russian interference in the US election.

"Every action we take will be designed to ensure our military is ready to fight today and in the future."

"Recognizing that no nation is secure without friends, we will work with the State Department to strengthen our alliances," he said, a contrast to Trump's recent branding of the NATO military alliance as "obsolete."

Lawmakers passed a special waiver allowing Mattis, who retired in 2013, to serve before a customary seven-year limit on former military personnel assuming the Pentagon's top post.

John Kelly, another retired Marine general, was also confirmed and sworn in to head the Department of Homeland Security.

"These uniquely qualified leaders will immediately begin the important work of rebuilding our military, defending our nation and securing our borders," Trump said in a statement.

"I am proud to have these two American heroes join my administration."

Mattis has won accolades from both parties and many in the armed forces, and his path to Trump's cabinet was relatively uncontroversial compared to that of other nominees.

A cornerstone of US democracy is that civilians, not people in uniform, control the military, and the commander-in-chief is the president.

Some in Congress initially raised eyebrows because Mattis, a 66-year-old Washington state native, had only retired from active duty in 2013.

The waiver allowing him to take the top Pentagon post was only granted once before, for the famous World War II general George Marshall who served under President Harry Truman from 1950-1951.

Mattis is known as a colorful commander and famed for his pugnacious aphorisms. The media dubbed him "Mad Dog" for his battle-hardened swagger and the sort of blunt language Marines are famous for.

He has been quoted as saying, "Be polite, be professional, but have a plan to kill everyone you meet."

But Mattis also has a well-known cerebral side: he issued reading lists to Marines under his command, and instructed them that the most important territory on a battlefield is the space "between your ears."

While Mattis sailed through his confirmation, Democratic lawmakers are putting up stiff resistance to other Trump cabinet picks, including nominees to head the departments of education and health and human services.

Mattis replaces Ashton Carter, a longtime Pentagon bureaucratic warrior who served as former president Barack Obama's fourth defence secretary.