MANILA — President Rodrigo Duterte of the Philippines said on Monday that he might not accept President Trump’s invitation to visit the White House, because he was “tied up” with a busy schedule.

“I cannot make any definite promise,” Mr. Duterte said, adding, “I’m supposed to go to Russia; I’m also supposed to go to Israel.”

Mr. Trump’s invitation on Saturday to Mr. Duterte, an authoritarian leader who has been accused of ordering extrajudicial killings of drug suspects, drew criticism from human rights advocates, who said such a visit would amount to a White House endorsement of Mr. Duterte’s policies. Thousands of people have been gunned down in the Philippines since Mr. Duterte took office in June, promising a crackdown on narcotics.

White House officials said Mr. Trump had called Mr. Duterte in an effort to mend their countries’ recently strained relationship, as a bulwark against China’s expansionism in the South China Sea. Reince Priebus, the White House chief of staff, said Mr. Trump also wanted to build a united front in Asia in opposition to North Korea’s pursuit of nuclear and missile technology.