A delegation of former U.S. defense officials is visiting Taiwan this week in a sign of stepped-up communication between the sides amid the looming threat from China.

Former Chairman of the Joint Chiefs of Staff Michael Mullen is leading the five-person delegation that is due to arrive later Tuesday and is scheduled to meet with President Tsai Ing-wen and other top officials during the two-day visit.

Separately, former Secretary of State Mike Pompeo was due to arrive in Taiwan on Wednesday. Pompeo, who also formerly led the Central Intelligence Agency, will also meet with Tsai and address a forum prior to his departure Saturday, according to the Foreign Ministry.

“Former secretary of state Pompeo's visit displays fully U.S. bipartisan backing for its ‘rock solid' support" for Taiwan, the ministry said.

Russia’s invasion of Ukraine has drawn fresh attention to China’s threat to use force to annex self-governing democratic Taiwan, which it claims as its own territory.

Circumstances are very different, however: Taiwan lies 160 kilometers (100 miles) across the turbulent Taiwan Strait from mainland China and enjoys strong support from the U.S., which is legally bound to ensure the island can defend itself and treat all threats to it as matters of “grave concern."

China has been sending military aircraft into Taiwan's air defense identification zone on a near-daily basis, and on Saturday, its Defense Ministry protested as provocative the passage of the guided-missile destroyer USS Ralph Johnson through the Taiwan Strait.

The Strait is in international waters and the U.S. Navy said the ship’s passage “demonstrates the United States’ commitment to a free and open Indo-Pacific."

China routinely protests U.S. contacts with Taiwan's government and in November, announced that its military conducted air and naval readiness patrols in the direction of the Taiwan Strait after five U.S. lawmakers met with Tsai on a surprise one-day visit.

President Joe Biden has followed his predecessors in stepping up contacts between Taiwan and both serving and retired administration officials, along with selling defensive military equipment.

The other members of Mullen's delegation are former Under Secretary of Defense for Policy Michele Flournoy, former White House Deputy National Security Adviser Meghan O’Sullivan, former Senior Director for Asia at the White House National Security Council Michael Green, and Evan Medeiros, former senior director of Asian affairs at the White House National Security Council.