Two masked men have set the offices of a prominent Mexican newspaper on fire, the second such attack on the daily in the last few weeks

The armed men walked into the Sierra Madre office of the El Norte newspaper in the northern city of Monterrey, threatened a security guard, poured gasoline out of canisters and lit the building on fire, the newspaper said. Fifteen people were working in the office at the time. Since Mexico declared an open war on drug cartels, journalists have been kidnapped, killed and threatened - particularly those who cover drug trafficking and institutional corruption. Since 2000, more than 70 journalists have been killed in the country.