MANILA - Opposition Senator Leila de Lima on Monday celebrated her birthday in detention, vowing to resist an alleged culture of impunity and breakdown of the rule of law.

De Lima has been detained at the police Custodial Center since February 2017 for allegedly accepting drug money from convicted crime lords when she was still justice secretary. A fierce critic of the administration's anti-narcotics drive, the senator rejected the allegation, saying this was politically-motivated.

"I will continue to defy my oppressors. I shall defy any lure of hopelessness," she said in a statement.

"I will resist the breakdown of the rule of law. I shall defy the enemies of truth and democracy. I will resist the rise of a culture of impunity."

De Lima celebrated the eve of her 58th birthday on Sunday with a Holy Mass attended by Senators Antonio Trillanes IV and Risa Hontiveros, Reps. Gary Alejano, Edgar Erice and Erin Tanada, lawyers Florin Hilbay and Barry Gutierrez, former elections chief Sixto Brillantes Jr., former social welfare secretary Dinky Soliman, and former peace adviser Ging Deles, among others.

De Lima said she was grateful for the support of her family, staff, and colleagues "who continue to fight with me and for me."

"To my former colleagues in the Cabinet, I am grateful that in your little ways, you continue to show to the public how important it is to have an ethical kind of leadership. I am also thankful na andiyan kayo (you're still there), still fighting with me," she added.

De Lima will launch a book featuring writings, speeches, letters about her and other personalities to mark her birthday.