KUALA LUMPUR - A Malaysian court on Monday upheld death sentences handed down to nine men from the Philippines in connection with an 2013 incursion into the Malaysian part of Borneo island by Philippine fighters seeking to stake an ancient claim.

The incursion by the fighters from the southern Philippines into Malaysia's Sabah state sparked a month-long crisis and at least 27 people were killed when Malaysian troops backed by fighter jets eventually subdued the militants.

The conflict disrupted operations in Sabah’s huge palm oil industry and at the time, raised concern that prolonged trouble could dampen investor interest in energy and infrastructure projects in the state.

The nine were among fighters captured.

• READ: DFA denies PH offered Sabah to win Malaysia's support

A five-member Federal Court panel unanimously ruled that the death sentences were the most appropriate, upholding a decision by a lower court to increase the penalty from life sentences, according to the state news agency Bernama.

The court also upheld a lower court's decision to release 14 other men who had been held in connection with the fighting in the sleepy Lahad Datu district.

The fighters were from a group that has demanded recognition, and an increased payment from Malaysia, for their claim to be the rightful owners of Sabah, which an ancient sultanate leased to British colonialists in the 19th century.

Malaysia dismissed their demands and the Philippine government repeatedly told the group to put down their weapons and go home.

The fighters declared loyalty to the self-proclaimed Sultan of the southern Philippine region of Sulu, Jamalul Kiram, in the Philippines.

• READ: PH, Malaysia put Sabah dispute on 'back burner'