Taiwan’s Defense Ministry said Tuesday it had detected 59 Chinese military aircraft and nine navy vessels operating around the island over the past 24 hours as part of “joint combat patrols,” days after the democratic island’s president called Beijing “a foreign hostile force.”

The aircraft tally was the highest reported for a single day near Taiwan since October, when China’s military held massive drills around the island. The Defense Ministry in Taipei said it was closely monitoring the exercises.

China’s Foreign Ministry said the move was intended as a warning to Taipei and “external forces” backing its formal independence — a veiled reference to the United States.

“It's a firm response to external forces who are hellbent on abetting and aiding ‘Taiwan independence,’ and a warning to ‘Taiwan independence’ separatist forces' unconscionable acts,” ministry spokesperson Mao Ning said Monday.

Taiwan’s Foreign Ministry condemned the latest exercises in a statement Monday night, saying China was “undermining stability in the region.”

Last Thursday, Taiwanese President Lai Ching-te branded China a "foreign hostile force," as he laid out measures to combat what he said was Beijing’s deepening infiltration of the island.

On Monday, Mao also pointed to "a series of wrong actions” by the U.S., including the State Department’s decision to delete a phrase from a fact sheet on Taiwan saying the U.S. does "not support” the island’s independence.

China views democratic Taiwan as its “core of core issues” and regards the island as a renegade province that must be unified with the mainland, by force if necessary. The Asian powerhouse has also lashed out at the U.S., claiming it has been eroding its commitments to Beijing on Taiwan and aiding a Taiwanese push for formal independence.

The United States switched diplomatic recognition from Taipei to Beijing in 1979, but has maintained unofficial relations with Taiwan and is bound by law to supply the island with weapons to help it defend itself.

The U.S. has over the years largely maintained a policy of “strategic ambiguity” as to whether or not it would come to Taiwan’s defense in the event of any attack or invasion by China, a stance U.S. President Donald Trump has so far appeared to stick with despite fears that he might break with the policy and demand that Taipei pay more for its protection.

Late last month, Trump declined to comment when asked whether it was the policy of his administration to prevent China from using force to take control of Taiwan.

The U.S. president’s refusal to comment on defending Taiwan stood in stark contrast to his predecessor, Joe Biden, whose administration had often called out China over its ramped-up military exercises near and around Taiwan. Biden also repeatedly hinted that Washington would come to Taipei’s aid in the event of a Chinese attack.

Senior Taiwanese officials have suggested that the Trump administration will continue to support the island.

“We need the U.S. support to sell us the most advanced weapons, and also to help train our soldiers, and they are doing that,” Hsu Szu-chien, deputy secretary general of Taiwan’s National Security Council, told Bloomberg News on Monday.

“We don’t expect the U.S. or anyone else to fight our war, we will fight our own war,” he added.