By Doina Chiacu and James Oliphant
WASHINGTON (Reuters) -The United States and NATO on Sunday condemned Russian President Vladimir Putin's order to put his nuclear forces on high alert as dangerous and unacceptable, while the White House said it has not ruled out imposing new sanctions on Russia's energy sector.
In issuing the order to prepare Russia's nuclear weapons for increased readiness for launch, Putin cited "aggressive statements" from NATO allies and widespread sanctions imposed by Western nations.
The U.S. ambassador to the United Nations, Linda Thomas-Greenfield, told CBS's "Face the Nation" program that Putin's actions have escalated the conflict and were "unacceptable."
Thomas-Greenfield said the United States was "continuing to look at new and even harsher measures against the Russians."
At the Pentagon, a senior U.S. defense official also described Putin's nuclear order as an escalation and said it was "putting in play forces that, if there's a miscalculation, could make things much, much more dangerous."
The United States is trying to determine what Putin's order means "in tangible terms," the official said, speaking on condition of anonymity.
On CNN's "State of the Union" program, NATO Secretary-General Jens Stoltenberg called Putin's nuclear order "aggressive" and "irresponsible."
White House Press Secretary Jen Psaki said Putin was responding to an imaginary threat.
"We've seen him do this time and time again. At no point has Russia been under threat from NATO, has Russia been under threat from Ukraine," Psaki said on ABC's "This Week" program.
U.S. APPEALS TO CHINA
The United States has not taken sanctions targeting Russia's energy sector off the table, Psaki said.
"But we also want to do that and make sure we're minimizing the impact on the global marketplace and do it in a united way," she added.
The Biden administration has worried that its sanctions could raise already-high gas and energy prices in the United States and has taken steps to mitigate that. When it issued sanctions targeting major Russian banks on Thursday, it allowed an exception for energy-related transactions.
In the administration's most urgent public appeal yet to China, Psaki urged the Communist state to issue a formal condemnation of Russia's invasion.
"This is not a time to stand on the sidelines," Psaki said on MSNBC. "This is a time to be vocal and condemn the actions of President Putin and Russia invading a sovereign country."
Chinese Foreign Minister Wang Yi said on Friday that China respects countries' sovereignty, including Ukraine's, but that Russia's concerns about NATO's eastward expansion should be properly addressed.
Meanwhile, Republicans in Congress continued to take an increasingly sharp tone toward Putin, showing that for now both parties are largely backing the Biden administration's efforts.
Representative Kevin McCarthy, the top Republican in the House of Representatives, told the Fox News Channel following the Russian president's nuclear order that "no country in the world should stand with Putin."
On CNN, Senator Mitt Romney, a former Republican presidential nominee, called Putin "a small, evil feral-eyed man who is trying to shape the world in the image where once again Russia would be an empire - and that's not going to happen."
U.S. Secretary of State Antony Blinken on Sunday announced $54 million in new humanitarian aid for Ukrainians affected by the invasion, which was in addition to the $350 million sent by the United States last week.
"This includes the provision of food, safe drinking water, shelter, emergency health care, winterization, and protection," Blinken said in a statement.
Senator Chuck Schumer, the Senate's majority leader, said the White House's request for an additional $6.4 billion in aid would be taken up by the Senate in the coming days.