President Trump acts swiftly

President Donald Trump assumed power on Friday with a fiercely nationalistic vow to put "America First," taking a stinging swipe at the legacy of his predecessor hours after reciting the oath of office.

Hundreds of thousands of people stood on the rain-splattered National Mall to see the 70-year-old Republican billionaire be sworn in, and deliver a stridently populist call-to-arms.

Trump promised to lift up the nation's disenfranchised and those who felt betrayed by the political elites, declaring with vindication that "the forgotten men and women of our country will be forgotten no longer."

Adhering to his vow to immediately start dismantling the healthcare reforms passed by president Barack Obama, Trump signed his first executive order in the Oval Office, targeting Obamacare.

It commands government offices to grant all possible exemptions to limit the "economic and regulatory burden" of the Affordable Care Act, as a prelude to a full repeal.

The Trump administration will also make defeating "radical Islamic terror groups" its top foreign policy goal, according to a statement posted on the White House website moments after Donald Trump's inauguration.

In the statement, titled "America First Foreign Policy," the Trump administration said, "Defeating ISIS and other radical Islamic terror groups will be our highest priority."

In order to "defeat and destroy" Islamic State and similar groups, the new administration said it "will pursue aggressive joint and coalition military operations when necessary," work to cut off funding for terrorist groups, expand intelligence sharing, and use "cyberwarfare" to disrupt propaganda and recruitment efforts.

Meanwhile, the first two Trump cabinet members were sworn in after being confirmed on Friday by the US Senate. Both are retired generals: Secretary of Defence James Mattis and Homeland Security Secretary John Kelly.

Trump also signaled a sharp break on energy and the environment policy, announcing plans to undo climate policies and promote domestic energy development as part of his "America First" agenda.

A statement on the White House website, posted shortly after Trump took the oath of office, said he was "committed to eliminating harmful and unnecessary policies such as the Climate Action Plan" advocated by his predecessor Barack Obama.

The official White House website on Friday deleted nearly all mentions of climate change. The one exception: Trump's vow to eliminate the Obama administration's climate change policies, which previously had a prominent and detailed web page on whitehouse.gov.

At the same time, the official White House Twitter handles also changed over, allowing Trump to now post on Twitter as @POTUS.

Trump during the campaign dismissed climate change as a "hoax" perpetrated by China.

During his inaugural address, Trump vowed that his presidency would usher in a new political era.

Moments earlier, the incoming US leader had placed his left hand on a bible used by Abraham Lincoln and recited the 35-word oath spoken since George Washington.

The popular turnout was visibly smaller than for Obama's two inaugurations, in 2009 and 2013, with sections of the mall and bleachers along the parade route left nearly empty.

Throngs of Trump's opponents also converged on Washington.

Most of their protests -- by an array of anti-racist, anti-war, feminist, LGBT, and pro-immigration groups -- were peaceful, but sporadic violence marred the day.

Several hundred masked, black-clad protesters carrying anarchist flags smashed windows, lit fires and scuffled with riot police blocks from the parade held in Trump's honor, with at least 217 people arrested for vandalism.

Even the peaceful protesters were intent on spoiling Trump's party -- letting out a deafening roar as the presidential limousine rolled past.

"Not my president! Not my president!" they yelled, as the pro-Trump crowd in nearby bleachers chanted "USA! USA!"

And yesterday, women in pink "pussyhats" flooded into Washington by the train-load for a massive rights march set to draw hundreds of thousands in defiance of America's hardline new president.

Metro stations overflowed as trains packed to bursting moved cheering, clapping marchers into the city for what was expected to be a record-breaking inauguration-related protest.

For Trump's critics, there was disbelief that a man who 19 months ago hosted "The Apprentice" reality TV show is now leader of the free world -- sworn in with a 37 percent approval rating, the lowest on record, according to a CBS News poll.

Meanwhile, Moscow has attempted to distance itself from Trump, saying the Republican is “not our man”.

Many Russians view Trump's presidency with high hopes, and some nightclubs and bars held parties to celebrate the inauguration.

President Putin's press secretary Dmitry Peskov told Russian state broadcaster Vesti: “He is not our man, he is America's man.”

Meanwhile, Craftsmen in the city of Zlatoust, east of Moscow, have released a limited series of silver and gold commemorative coins, engraved with "In Trump We Trust" -- an allusion to the phrase on US banknotes "In God We Trust," reports Reuters.

The commemorative coin was created by Art Grani. It features the face of Trump on one side and the Statue of Liberty on the other. Only 45 exist: 25 silver coins, 5 gold and 15 that are silver and gold, according to CNN. 

Trump's inauguration caps the improbable rise of the Manhattan real estate magnate who has never before held elected office, or served in government or the military.

For the next few weeks the White House plans a series of daily executive orders to roll back Obama's agenda.

Trump has also vowed to re-examine long-running alliances with Europe and in Asia.

"We will reinforce old alliances and form new ones and unite the civilized world against radical Islamic terrorism, which we will eradicate completely from the face of the Earth."

The statement vowed to "rebuild" the American military, including enlarging the Navy and the Air Force, a frequent theme during Trump's campaign.

The statement vowed to "rebuild" the American military, including enlarging the Navy and the Air Force, a frequent theme during Trump's campaign.

The White House statement also vowed to withdraw from the Trans-Pacific Partnership, the Asian free-trade pact that Obama championed but was unable to get through Congress. Trump has said, without elaboration, that international trade deals have hurt American workers.

In a separate statement on the White House website, the Trump administration said it intends to develop a "state of the art" missile defense system to protect against attacks from Iran and North Korea. It did not say whether the system would differ from those already under development, specify the cost or say how it would be financed.