Several Taiwan media outlets reported late on Monday that US House of Representatives Speaker Nancy Pelosi will visit Taiwan on Tuesday and spend the night in Taipei, citing unidentified sources.

China has warned that its military would never “sit idly by” if Pelosi were to visit Taiwan, the self-ruled island claimed by Beijing.

The Liberty Times newspaper said Pelosi was scheduled to visit Taiwan’s parliament on Wednesday morning before continuing her Asia trip.

The United Daily News, also citing unnamed sources, said “related officials” were told to receive Pelosi, who is set to arrive in the capital Taipei on Tuesday evening at the soonest and spend the night there.

Taiwan’s foreign ministry said it has no comment on reports on Pelosi’s travel plan and no further information to share with media.

Earlier on Monday, Chinese foreign ministry spokesman Zhao Lijian said it would be “a gross interference in China’s internal affairs” if Pelosi visits Taiwan, and warned that it would lead to “very serious developments and consequences.”

A visit by Democrat Pelosi, who is second in the line of succession to the US presidency and a long-time critic of China, would coincide with worsening ties between Washington and Beijing. Republican Newt Gingrich was the last US House speaker to visit Taiwan, in 1997.

Beijing considers Taiwan to be part of its territory and has never renounced using force to bring the island under its control. Taiwan rejects China’s sovereignty claims and says only its people can decide the island’s future.