Nikki Haley on Saturday called Aleksei A. Navalny, the outspoken Russian opposition leader, “a hero” and amped up the pressure on former President Donald J. Trump to respond to the news of his death. She said Mr. Navalny had died at the hands of President Vladimir V. Putin and that Mr. Trump needed to “answer to that.”

Speaking with reporters outside her rally at a park in Irmo, S.C., Ms. Haley praised Mr. Navalny for calling out Mr. Putin for corruption and fixing elections. She said he had fled his country only to return “to fight the good fight.”

“And then he was arrested, and now Putin has done to him what Putin does to all of his opponents — he kills them,” she said, before turning to Mr. Trump, her rival in the G.O.P. primary. “And Trump needs to answer to that. Does he think Putin killed him? Does he think Putin was right to kill him? And does he think Navalny was a hero?”

Ms. Haley, the former governor of South Carolina and a United Nations ambassador under Mr. Trump, has been running on her foreign policy experience and has long criticized her former boss over what she has described as his love of dictators and authoritarian leaders. She has only continued to ratchet up the criticism of him as they head into a primary showdown in her home state on Feb. 24.

Mr. Trump has not yet commented publicly on Mr. Navalny’s death. On Saturday he did attack President Biden and said in a post online that “I am the only one who can bring Peace, Prosperity, and Stability like I did during my first term. America will be respected and feared (if necessary!) again.”

On Friday, soon after the news of Ms. Navalny’s death broke, Ms. Haley went further than most Republicans in attacking Mr. Trump for his past remarks in praise of Mr. Putin. At her rallies since, she has underscored Mr. Trump’s cozy relationship with the Russian leader and sought to sound the alarm over his suggestions that he would encourage Russian aggression against U.S. allies in Europe.

On Saturday, she also addressed the news that Russia was developing a nuclear space weapon with the potential to destroy satellites, calling for the prevention of war in space.

Russian authorities announced on Friday that Mr. Navalny, who was serving multiple sentences in Russia, had died in a prison inside the Arctic Circle. President Biden has said that U.S. officials did not have a full understanding of the circumstances, but that he believed that “there is no doubt that the death of Navalny was a consequence of something that Putin and his thugs did.”

In the news conference on Saturday, Ms. Haley asked of Mr. Trump: “Why does he always side with dictators?”