Story highlights A Taiwanese fisherman was killed by gunfire from a Philippine coast guard vessel last week

Taiwan's president describes it as a "cold-blooded murder"

The Philippines says the fisherman's death was "unintended"

Taiwan has imposed a series of punitive measures to show its displeasure

May has been a bad month for relations between Taiwan and the Philippines.

Taiwan has reacted angrily after one of its fishermen was killed by a Philippine coast guard vessel last week. It has recalled its diplomatic envoy from Manila, frozen applications from Filipinos seeking to work in Taiwan and held naval drills near Philippine waters.

The Philippine coast guard has said the crew of one of its ships fired at the Taiwanese fishing boat on May 9 after it tried to ram a Philippine boat. Manila insists that the shooting took place in waters inside its exclusive economic zone and that the loss of life was "unintended."

But Taiwan says the Philippine vessel sprayed the fishing boat with bullets in waters claimed by the exclusive economic zones of both countries. It says the 65-year-old fisherman, Hung Shih-cheng, was fatally shot in the back.

The souring ties between the two countries are born out of the messy mix of competing territorial claims to parts of the South China Sea and nearby waters by Brunei, China, Malaysia, the Philippines, Taiwan and Vietnam. The areas in dispute include fertile fishing grounds and potentially rich reserves of undersea natural resources.

President Ma Ying-jeou of Taiwan on Friday described last week's shooting as a "cold-blooded murder," the Taiwanese national news agency CNA reported.

Ma has so far deemed the Philippine response to the killing to be unsatisfactory. His government has demanded that Manila make a formal apology, compensate the losses, investigate and punish those responsible, and start talks between the two countries on a fishing agreement.

Among the series of measures Taiwan has imposed this week to show its displeasure is a travel alert urging its citizens not to visit to the Philippines.

The Philippine government, meanwhile, has started to show frustration with the Taiwanese stance.

"We did what a decent member, a respectable member of the international community should have done," Edwin Lacierda, a spokesman for President Benigno Aquino III, said Thursday. "We have gone the extra mile."

Aquino sent "a personal representative to extend his apology" and offer financial assistance to the family of the dead fisherman, Lacierda said, according to CNN affiliate ABS-CBN. Philippine authorities are investigating the shooting, he said.

He warned that the measures imposed by the Taiwanese government would hurt the economies of both countries.

Lacierda also appealed to the Taiwanese people not to hurt Filipinos living in Taiwan amid reports of harassment.

But Garfie Li, a spokeswoman for Ma, said Lacierda's comments about going the extra mile were "were untrue and totally unacceptable," according to CNA.

The United States, an ally of both the Philippines and Taiwan, has expressed regret" over the fisherman's death and urged the two sides "to work together and to ensure maritime safety, and refrain from actions that could further escalate tensions."

China has supported Taiwan, which it views as a breakaway province.

"We have repeatedly condemned the violent killing of the innocent fisherman since the incident happened," Yang Yi, a spokesman for the State Council's Taiwan Affairs Office, said Wednesday, according to the state-run news agency Xinhua. "We have demanded that the Philippine side take the case seriously, find out the truth as quickly as possible and punish those responsible."

Beijing and Manila are already at odds over a different territorial dispute in the region that led to a maritime standoff last year.