By Mi Nguyen

HANOI (Reuters) - Vietnam began the trial on Monday of 22 executives charged over losses at the state oil firm, including a businessman Germany accuses Hanoi of kidnapping from a Berlin park and the communist state's first politburo member to face trial in decades.

The most serious offences could carry the death penalty for the executives accused over losses at state oil firm PetroVietnam.

A widespread crackdown on fraud and mismanagement in the energy and banking sectors has gathered pace since the security establishment gained greater influence in the ruling party last year.

The trial opened under high security at the Hanoi People's Court. Crowds gathered outside but there was no public access.

Of the 22 executives on trial, 12 are accused of "violation of state regulations on economic management causing serious consequences". Eight are accused of embezzlement, according to the government's official news website. Some are accused of both.

The most senior former executive on trial is Dinh La Thang, who was arrested last month. He is a former politburo member who was dismissed from his post over the losses at PetroVietnam and then stripped of his role as party head of Ho Chi Minh City.

Also on trial is Trinh Xuan Thanh, who Germany says was kidnapped last year and taken home against his will to face accusations over losses of more than $150 million at a subsidiary of PetroVietnam.

Thanh is accused of both corruption and breaking state rules on economic management. A Reuters reporter saw Thanh arrive at the court on Monday wearing glasses and being escorted inside by police in green uniforms.

Thanh appeared on state television in August and said he had decided to return home and turn himself in.

Neither Thang nor Thanh made any comment at the court and Reuters was unable to contact the lawyers representing them.

The maximum jail term for deliberate violation of state regulations is 20 years in prison, state television VTV1 reported in a news bulletin on Monday.

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Government critics have voiced suspicions that the corruption crackdown is politically motivated, at least in part, and aimed against those close to former prime minister Nguyen Tan Dung, who lost out in an internal power struggle in 2016.

The trial is due to last until Jan. 21.

In a separate case linked to the corruption crackdown, a fugitive Vietnamese tycoon was arrested in Hanoi on Thursday after being sent home from Singapore, where he was accused of immigration offences.

Phan Van Anh Vu, 42, told his lawyers he was also a senior officer in Vietnam's secret police and was trying to get to Germany and could have details of the operation in which Thanh was spirited home from Berlin last year.

A separate trial that is part of the government's wider corruption crackdown began on Monday in the commercial capital Ho Chi Minh City. Forty-six people went on trial over allegations related to a fraud case at Vietnam's Construction Bank.

(Writing by Matthew Tostevin; Editing by Amy Sawitta Lefevre and Paul Tait)