UPDATE 1-Argentina's Milei taps conservative ex-rival Bullrich as security tsar

(Updates with additional detail)

BUENOS AIRES, Dec 1 (Reuters) - Argentine President-elect Javier Milei has picked conservative election campaign rival Patricia Bullrich as his security minister, his office said on Friday, another signal of the outsider libertarian selecting a more moderate first Cabinet.

Bullrich, who was the candidate for the main conservative opposition bloc, had been an early favorite in the polls to win the presidential election, but failed to reach the runoff between Milei and Peronist Economy Minister Sergio Massa.

She then threw her weight behind Milei in the second round, bringing most of her center-right coalition with her and helping Milei post a strong win in the head-to-head vote last month. The new government will take office on Dec. 10.

Bullrich, security minister before under former President Mauricio Macri (2015-19), had promised a tough-on-crime stance in her campaign, and offered more of the same on Friday.

"Argentina needs order," she said in a statement following her nomination. "We will be relentless against crime and we will wage a relentless fight against drug trafficking."

The Latin American nation is currently battling an economic crisis with triple-digit inflation, net reserves deep into the red and a $44 billion program with the International Monetary Fund (IMF) which has veered off track. (Reporting by Gabriel Araujo and Lucila Sigal; Editing by Kylie Madry)