BEIJING — President Tsai Ing-wen of Taiwan sharply criticized China’s leaders on Saturday, saying they had resorted to military and economic threats in order to intimidate the island.

“Step by step, Beijing is going back to the old path of dividing, coercing and even threatening and intimidating Taiwan,” she told journalists in Taipei, the capital, at a year-end news conference.

Tensions between Taiwan and China, which have been rivals since the Communist Revolution of 1949, intensified in December after Ms. Tsai spoke on the phone with the American president-elect, Donald J. Trump, breaking a longstanding diplomatic practice.

In recent weeks, China has stepped up military activities near Taiwan, sending its sole aircraft carrier through the waters near the island and dispatching military planes in the region. On Monday, Beijing announced that São Tomé and Príncipe, an island nation off the west coast of Africa that was one of Taiwan’s fewer than two dozen remaining diplomatic allies, had switched its allegiance to the mainland, provoking an outcry in Taiwan.