Beijing on Thursday expressed concern after Myanmar handed long jail sentences to more than 150 Chinese nationals for illegal logging, in the latest tremor to shake relations between the neighbours.
The mass sentencing, which has sparked outraged editorials in Chinese state-run media, comes after the loggers were arrested in January during a crackdown on illegal forestry activities in northern Kachin state, which borders China.
For years China has hoovered up Myanmar's once abundant raw materials, spurring popular anger in the former junta-ruled country which is set for a general election later this year.
Beijing has asked its smaller neighbour to "deal with this case in a lawful, reasonable and justified manner... and return those people to China as soon as possible", foreign ministry spokesman Lu Kang said in a statement on the ministry's website.
An unnamed Myanmar court official in Kachin state told AFP on Wednesday that 153 Chinese loggers had been jailed for life for illegal logging. Life in Myanmar is equivalent to 20 years according to legal experts.
He said a further two boys under 18 were handed 10-year sentences without giving details, while a woman was jailed for 15 years on narcotics charges.
The statement from Beijing's foreign ministry said it "lodged multiple representations on different levels and through various channels" since the arrests in January.
An editorial in China's Global Times slammed the "severity" of the sentences, expressing hope that intervention from Beijing could "reverse" the outcome.
"A few cases of Chinese engaging in illegal business in Myanmar have been scrutinized by public opinion, exaggerated as China's economic 'invasion' of the latter," it said, urging the Myanmar public "to look upon China-Myanmar trade in a positive way".
It is the latest spat to sully ties between the two countries.
Beijing was Myanmar's closest ally during the later years of military rule, providing a shield from international condemnation and a lifeline as a trading partner for a junta that badly mismanaged the economy.
But observers say the scale of interests China accrued during that period—from dams and mines, to a gas pipeline aimed at developing its southern Yunnan province—caused friction and prodded Myanmar towards reforms in an effort to balance Beijing's power.
Those reforms, started in 2011, have seen the rollback of most western sanctions and the promise of a foreign investment boom.
A general election on November 8 is being keenly watched as a marker of the extent of Myanmar's liberalisation.
One of the first major acts of President Thein Sein, whose quasi-civilian government replaced outright military rule, was to halt construction of the huge Chinese-backed Myitsone dam in Kachin, where a bloody civil war has raged since 2011.
Thein Sein faced anger from Beijing in March after a Myanmar plane dropped a bomb in Chinese territory leaving five Chinese citizens dead as fighting between government troops and ethnic Chinese Kokang rebels spilled across the border.
Logging in Myanmar exploded under the country's former junta as the ruling generals tossed aside sustainable forestry practices in a rush to cash in on the country's vast natural resources—with vast areas stripped bare, partly to feed huge demand across the border in China.
Thein Sein's government has sought to stem the flood of timber from the country with a ban on the export of raw logs that came into effect in April last year.
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