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MEXICO CITY (Reuters) - Mexico’s Pemex said on Thursday it had launched a tender offer to prepay around a third of $14.7 billion in bonds maturing between 2020-2023, in President Andres Manuel Lopez Obrador’s latest effort to shore up the state oil firm.

The offer says Pemex is looking to prepay up to $5 billion of those bonds, using a major capital injection announced by the Mexican government for this purpose on Wednesday.

The offer will expire next Wednesday.

Pemex also offered $7.5 billion worth of bonds with maturities of seven, 10 and 30 years, news service IFR reported. It cited a source close to the deal who said Pemex had received $37 billion worth of offers.

Lopez Obrador, a veteran leftist who took power in December, has vowed to revive Pemex, a company that became an icon of Mexican self-sufficiency after it was created with the expropriation of foreign oil interests in 1938.

However, years of declining oil output, mismanagement and corruption have taken their toll on the firm, which is now the world’s most heavily indebted oil company, with $104 billion in financial debt.

The firm, formally known as Petroleos Mexicanos, is also fighting to avoid a second downgrade of its debt to junk status, after Fitch Ratings took that step in June.

To avert a further credit ratings downgrade, the Mexican government under Lopez Obrador has given Pemex tax breaks and cash support several times this year, and has budgeted for another $4.4 billion of similar support in 2020.