South Korea’s government was paralyzed Sunday, mired in a new constitutional crisis after President Yoon Suk Yeol of South Korea clung to his office, but his own party’s leader suggested that he had already been ousted from power.

Mr. Yoon has barely been seen in public since his ill-fated decision last week to declare martial law. Meanwhile, Han Dong-hoon, the chairman of Mr. Yoon’s People Power Party, or P.P.P., has presented himself as the government’s decision maker and said the president is no longer running the country.

The trouble is that South Korea’s Constitution doesn’t allow for anyone to replace the president unless he resigns or is impeached.

Mr. Yoon’s office did not comment on Mr. Han’s statement. But Mr. Yoon “has not and by law, cannot, cede power to anyone” except through resignation, impeachment or election, said a senior government source familiar with the discussions inside Mr. Yoon’s office.

Opposition groups immediately complained that Mr. Han was overreaching: trying to use the power vacuum created by Mr. Yoon’s ill-fated imposition of martial law and the ensuing turmoil to establish himself as the top leader in the governing camp.

“We have a situation where the president cannot make decisions, he cannot give guidelines, he cannot give orders,” said Kang Won-taek, a professor of political science at Seoul National University. “Although we have a president, we are in a state of anarchy.”