BRASILIA, March 26 (Reuters) - Brazil's tax agency said on Thursday that it and federal police have detected corrupt activities at the agency that could have cost state coffers at least 5 billion reais ($1.57 billion).

The tax agency allegations come on the heels of a probe that has uncovered a multibillion-dollar corruption scandal at state oil giant Petroleo Brasileiro SA, known as Petrobras, which has rattled Brazil's political establishment and weighed on the country's fragile economy.

The tax agency is part of Brazil's finance ministry.

The agency said in a statement that the investigation, which began in 2013, well before current Finance Minister Joaquim Levy took office, indicates "strong evidence" of influence peddling, corruption, criminal conspiracy and money-laundering.

($1=3.19 Brazilian reais) (Reporting by Alonso Soto, Editing by Brian Winter; and Peter Galloway)

Our Standards: The Thomson Reuters Trust Principles.