Taiwanese authorities said they had detained a cargo ship crewed by Chinese nationals, which investigators believe may have severed an undersea communications cable near the island on Tuesday. It was the latest in a series of murky incidents that have prompted theories that China and Russia may be turning to cable sabotage as a form of harassment at sea.

The cable that was damaged connected Taiwan to the Penghu Islands, which belong to Taiwan and lie about 30 miles west of the main island. Taiwan’s Coast Guard said that it was still investigating the latest incident and had not reached any conclusions about whether the severing was deliberate or accidental.

But Ou Yu-fei, a press officer for the coast guard, said initial clues pointed to the detained ship, a dilapidated cargo carrier that used more than one name, including “Hong Tai 58.” The ship had Chinese funding, the coast guard said in a statement.

“This was the only vessel in the area — that’s our judgment,” Mr. Ou said in a telephone interview, citing radar records of where the cable break occurred. “We’re not ruling out the possibility that it was engaged in an act of sabotage. We go by the evidence. It’s too early to reach conclusions.”

Mr. Ou added that the ship may have used a false registration number and appeared to have suddenly had its name changed, among other details.

The ship may have severed the cable — accidentally or deliberately — around the time that a Chinese coast guard ship warned it to leave the vicinity in the early hours of Tuesday, he said. “It is possible that it used the time when it was leaving to carry out sabotage,” he said.