US President Joe Biden signed the first ordinances in the Oval Office on Wednesday. Among them is a document reversing Donald Trump's decision to withdraw the US from the Paris climate agreement.
It will take 30 days for the U.S. to formally return to the Paris Climate Agreement.
Biden also signed a document that obliges him to wear masks in federal buildings.
One of his first signatures, the new president also intends to place orders withholding funds for the construction of a wall on the border with Mexico and the process of US withdrawal from the World Health Organization (WHO).
In the coming days, an ordinance lifting the ban on serving in the US military for transsexual people is also to be signed. Trump's US entry ban on passport holders from seven Muslim-majority countries will also be completed.
Biden said he received a letter left at the White House from his predecessor Donald Trump. "It was a private letter and I won't talk about it until I speak to him. But (the letter) was kind," he said.
Under unprecedented security measures, Biden was sworn in before the Capitol as the 46th president of the United States on Wednesday. The 78-year-old Democrat is the successor to Republican Donald Trump.
In his inaugural speech, a politician with nearly 50 years of experience called for national unity and spoke of the "triumph of the idea of democracy". (PAP)