Most tigers in Sumatra are killed for commercial gain, according to World Wildlife Fund. (File)

The skin of a critically endangered Sumatran tiger and four foetuses have been confiscated after the arrest of several suspected poachers, Indonesian police said.

The suspects may have been planning to sell the skin to a foreign collector, while its bones were earlier sold, possibly for use in medicinal products popular in some parts of Asia, authorities said.

It was not clear how the foetuses, which were kept in a jar, were to be used.

The evidence was presented by police at a press briefing Sunday after they announced three people had been arrested at the weekend.

"We suspect that they would sell the skin to collectors, not only in Indonesia," Edward Hutapea, wildlife enforcement chief in Pekanbaru on Sumatra island, told AFP on Monday.

The suspects had previously sold another tiger skin, but had yet to unload the second skin and foetuses, he said, adding that the unborn mammals were from the big cat sold earlier this year.

If convicted, the trio could face up to five years in prison.

Poaching is responsible for almost 80 percent of Sumatran tiger deaths, according to TRAFFIC, a global wildlife trade monitoring network.

Sumatran tigers are considered critically endangered by protection group the International Union for Conservation of Nature, with fewer than 400 believed to remain in the wild.