MANILA (Reuters) -The Philippine military chief urged Filipino fishermen to keep fishing in the country's exclusive economic zone in the South China Sea, despite China's new coastguard rules allowing it to detain trespassers without trial, which take effect on June 15.

China, which claims almost all of the South China Sea including parts claimed by the Philippines, Brunei, Malaysia, Taiwan and Vietnam, has issued new rules that would enforce a 2021 law allowing its coastguard to use lethal force against foreign ships in waters that it claims.

"That's our message to our fishermen, for them not to be afraid but to just go ahead with their normal activities in our exclusive economic zone," Armed Forces of the Philippines Chief Romeo Brawner told reporters on Friday.

"We have the right to exploit the resources in the area so our fishermen have no reason to be afraid," he added.

The new rules, which allows China's coastguard to detain suspected trespassers without trial for 60 days, have sparked international concerns, with the Philippines describing them as "worrisome" and a "provocation".

Taiwan's coastguard said in a statement "it will strengthen fishing protection tasks, resolutely defends the safety of our fishermen's operations and ensure the rights and interests of shipping, and defend national sovereignty".

It also called on China "not to use this reason to justify unilateral acts that undermine regional peace".

The United States, which has a mutual defence treaty with the Philippines and is bound by law to provide Taiwan with the means to defend itself, said Chinese domestic law "has no applicability to other states' flagged vessels in other states' exclusive economic zones or in the high seas, according to the 1982 Law of the Sea Convention.

"Enforcement would be highly escalatory and detrimental to regional peace and security," a spokesperson for the U.S. State Department added. "We've urged Beijing - and all claimants - to comport their maritime claims with international law as reflected in the 1982 Law of the Sea Convention."

China has stepped up military activities near democratically-governed Taiwan, which it views as its own territory. It is also involved in an increasingly bitter stand-off with the Philippines in the disputed South China Sea.

The Chinese foreign ministry has said previously the new rules were meant to protect the maritime order, and that there was no need to worry if there was no illegal behaviour by the individuals and bodies involved.

(Reporting by Karen Lema; Additional reporting by Ben Blanchard and David Brunnstrom; Editing by Alex Richardson and Chizu Nomiyama)