MANILA (Reuters) - The Philippines plans to file a strong protest against China after it announced preparatory work for an environmental monitoring station on a disputed shoal in the South China Sea, a Cabinet minister said on Tuesday.

Fishermen prepare to fish at disputed Scarborough Shoal at the coastal village of Cato in Infanta, Pangasinan in the Philippines, November 3, 2016. REUTERS/Erik De Castro

China five years ago started blockading the Scarborough Shoal, a rocky outcrop within the Philippines’ 200 mile exclusive economic zone (EEZ), and the United States has warned Beijing against carrying out the land reclamation work there.

Justice Minister Vitaliano Aguirre told reporters Manila would file a complaint against Beijing’s plan to install a radar station on Scarborough Shoal.

“The case which will be filed is fairly strong I think,” he said.

The Philippines would take necessary action to defend and protect the country’s sovereignty and entitlements in the disputed maritime borders, presidential spokesman Ernesto Abella said in a statement.

“President Rodrigo Duterte has repeatedly asserted that the Philippines is not giving up its claims and our entitlements over the area,” he said.

The mayor in charge of administration of disputed South China Sea islands and reefs China controls last week said preparatory work was being planned this year to build monitoring stations on a number of islands.

Duterte was asked on Sunday for his response to the report of a radar station to be built at the Scarborough Shoal and said: “We cannot stop China.”

He also said it was pointless going to war with China

China until late last year had two to three coastguard ships guarding the shoal and stopping Filipinos from tapping its vast fish stocks. An international tribunal ruled last year that Beijing violated Manila’s entitlements and no country has sole rights to fish there.

However, just days after Duterte visited China and heralded a new era of ties, Filipinos returned to fish at the periphery of the shoal, unimpeded by Chinese vessels.

Aguirre said the Philippines would renew its strong ties with Washington in the face of China’s aggressive action in the shoal, which is 124 nautical miles from nearest coast of the main island of Luzon.

“As a matter of fact, we’re strengthening the relationship with the United States,” he told reporters.

Last month, former Foreign Minister Perfecto Yasay said the U.S. had dissuaded China from reclaiming Scarborough Shoal, which security analysts consider a red line that could escalate tension in the region.

China has put missiles and radar on some of its seven manmade islands in another part of the South China Sea, a strategic water claimed by Brunei, Malaysia, the Philippines, Taiwan and Vietnam.

The U.S. stresses the importance of free navigation in the sea, through which more than $5 trillion worth of trade passes each year.