BEIJING (Reuters) – China sent fighter jets to the seas off Taiwan on Wednesday, the latest in a series of deployments that Beijing has given orders for the past two years, the latest sign of growing security and tension in the long-strained relationship.

Beijing is traditionally suspicious of its rival’s democratic movement and claims Taiwan as its own territory with the right to challenge it militarily. China acknowledges Taiwan has no formal military presence on the mainland and has used assertive words to the contrary.

Taiwan’s president welcomed the deployment by the People’s Liberation Army (PLA) Air Force and sent a condolence note to Beijing, the presidency said in a statement.

A White House spokesman said President Donald Trump had been “aware” of China’s warplanes flying close to Taiwan.

Chinese jets went near Taiwan in April and again in May, the U.S. embassy said. China’s military has begun deploying more aircraft over the contested South China Sea and islands in the East China Sea where it has rattled rival claimant nations.

But in recent months, Beijing has sent more fighters and bombers to the southern Taiwan island, and on Monday, another Chinese aircraft plane came close to Taiwan in international airspace, the presidential office said.

It said China would take further steps to expand military exchanges with Taiwan.

“China will continue to firmly implement its national policy regarding maintaining peace and stability on the island,” it said.

The presidential office did not elaborate.

Another Chinese plane was seen flying within 10 nautical miles of Taiwan’s airspace from 6:30 p.m. (1600 GMT) to 8:45 p.m. (1900-2000 GMT), the Taiwan government said.

The confrontation came after pro-independence legislators said they were preparing to gather at parliament after a three-year break to impeach the governor, Chen Shui-bian, over a land deal.

The PLA, which did not reply to a faxed request for comment, has the power to deploy military aircraft through an authorization based on the foreign policy and security guidelines of the state council.

Accusing Taiwan of engaging in military provocations, Chen said: “Taiwan’s defense policy is backed by a multifaceted consensus of the Taiwanese people, in accordance with the national interest.”

He added that “separate development (on Taiwan) cannot be a substitute for unification.”

Last month, Taiwan President Tsai Ing-wen visited the United States, emerging as the most outspoken advocate of negotiating a peaceful end to the 49-year conflict between the two sides, which have fought three wars since 1949, two over sovereignty and one for independence.

Chinese jets swooped about Taiwan in March, just days after six Chinese Navy ships sailed within 28 nautical miles of the island and brought anti-ship missile systems into international waters.

Beijing says this action was provocative and violated U.N. rules. Taiwan says it was for “security reasons”, accusing China of fanning tension in the divided island, whose population of 7.7 million is divided between supporters of independence and supporters of greater democracy.

China and Taiwan have been ruled separately since a civil war ended in 1949.