Indonesia last week announced plans to sink 51 vessels from Vietnam, Malaysia, the Philippines, Thailand and China at sea near Pontianak, West Kalimantan in two weeks. Over a dozen were scuttled on Saturday.

Indonesian authorities say the vessels have fished illegally in its waters, and the sinking is a "necessary action" to warn neighboring countries that Indonesia is serious about fighting illegal fishing.

Yet Vietnam stresses that Indonesia’s actions have seriously violated its sovereignty and jurisdiction.

Le Thi Thu Hang, the Ministry of Foreign Affairs spokeswoman, told the press on Thursday: "This is an action that is not suitable with Vietnam and Indonesia’s bilateral relationship, and goes against the 1982 United Nations Convention on the Law of the Sea (UNCLOS)."

Vietnam has cordially communicated with Indonesia multiple times through different channels on the issue of sinking Vietnamese vessels, said Hang.

Vietnam also asked Indonesia to act in accordance with international law, UNCLOS, and to treat Vietnamese vessels and fishermen humanely, as appropriate with the bilateral ties that Vietnam and Indonesia enjoy, and in keeping with ASEAN’s cooperative spirit.

"Vietnam would like to develop a friendly, cooperative, multifaceted relationship with Indonesia in the spirit of the two countries’ strategic partnership for the benefit of the people of both countries and the building of a united and strong ASEAN community, which contributes to peace, stability, cooperation and development in the region and the world," Hang said.

She said 17 Vietnamese vessels have been seized and 140 Vietnamese fishermen captured by Indonesia since the beginning of 2019.

Last year, Indonesia destroyed 86 Vietnamese fishing boats for allegedly illegally catching fish in its waters.

The tensions have risen this year as Indonesia arrested a group of Vietnamese fishermen fishing in Vietnamese waters, in an area where Vietnam and Indonesia are delimiting their exclusive economic zones (EEZs) on April 27. 

A Vietnamese fishing boat with 14 fishermen on board was seized and towed away at high speed by Indonesian ship number 381, causing the Vietnamese boat to sink. 12 fishermen were taken into Indonesian waters, while two were rescued by a Vietnam Fisheries Resources Surveillance's vessel. Vietnam has since demanded that Indonesia release the crew of the sunken vessel and duly compensate them.