Armed men firing from pickup trucks and flying a helicopter attacked Brazil's most-secure prison in an attempt to free some of the lockup's high profile inmates but were driven away by guards, authorities said Monday. The federal prison attacked late Sunday houses two of Brazil's most notorious inmates, Colombian drug lord Juan Carlos Ramirez Abadia and Brazilian gang leader Luiz Fernando da Costa. An investigation is under way to determine whether the attackers were trying to free Ramirez Abadia, da Costa or other inmates, said a justice ministry spokesman who declined to give his name in keeping with department policy. The spokesman said the helicopter overflew the prison during the attack but never landed. All of the attackers got away and no one was injured at the prison, located in the Mato Grosso do Sul state capital of Campo Grande in southwestern Brazil. Ramirez Abadia - nicknamed "Chupeta," or "Lollipop" - is accused of leading the powerful Norte del Valle cartel, which emerged as Colombia's most powerful drug gang in the mid-1990s. A Brazilian judge found him guilty of money laundering, corruption, conspiracy and use of false documents.