The Philippine Navy reported Tuesday that 18 Chinese vessels maintained their presence in parts of the West Philippine Sea (WPS) over the past week.

Navy spokesperson Rear Adm. Roy Vincent Trinidad said the vessels were monitored from 15 to 22 February.

He said four People’s Liberation Army (PLA) Navy vessels and five China Coast Guard ships were spotted near Bajo de Masinloc, while four China Coast Guard vessels were seen near Ayungin Shoal.

Three vessels — two from the PLA Navy and one from the China Coast Guard — were monitored near Escoda Shoal, while two others, one PLA Navy and one China Coast Guard ship, were seen near Pag-asa Island.

The report followed a statement by the Philippine Coast Guard on Monday that China appeared to have engaged in signal jamming that disrupted communications of Philippine vessels conducting maritime patrols near Bajo de Masinloc.

Parts of the South China Sea within Philippine territory have been renamed the West Philippine Sea to reinforce the country’s maritime claims.

Trinidad said the West Philippine Sea covers maritime areas west of the Philippine archipelago, including the Luzon Sea and waters within and adjacent to the Kalayaan Island Group and Bajo de Masinloc.

In 2016, the Permanent Court of Arbitration in The Hague ruled in favor of the Philippines, declaring China’s expansive claims in the South China Sea to have no legal basis.

Tensions persist as China claims nearly the entire South China Sea, a major shipping route for more than $3 trillion in annual maritime trade, including areas also claimed by the Philippines, Vietnam, Indonesia, Malaysia and Brunei.