RIO DE JANEIRO (AP) — Brazil's minister of cities says there is a "strong link" between the country's woeful sanitation system and the current outbreak of the mosquito-borne Zika virus.

Gilberto Kassab said Wednesday that while the country has made progress over the past decade, sewage and water delivery systems leave "much to be desired," and promised that basic sanitation will continue to be a government priority.

Sewage often flows through open channels into stagnant waters, and a lack of piped water service leads many Brazilians to rely on tanks that create a habitat for the Aedes aegypti mosquito that transmits Zika, which has been linked to a rare birth defect called microcephaly which can leave babies with long-lasting health and developmental problems.

Kassab conceded the virus spread "has a strong link with the absence of sanitation," in quotes carried by the O Estado de S. Paulo daily.

His comments came at a news conference in the capital by the National Conference of Brazilian Bishops, which issued a statement blasting the government over water treatment, sewage and the collection of rubbish. The conference's head, Sergio da Rocha, said "the lack of basic sanitation is among the principal causes for the proliferation of mosquitoes."

Trata Brasil, a Sao Paulo-based pro-sanitation organization, says 35 million Brazilians, or around 18 percent of the population, do not have regular access to tap water. The group estimates that more than 60 percent of sewage nationwide flows untreated into waterways and onto the country's famed beaches.

Sanitation has become a hot-button issue here ahead of this year's Olympic Games in Rio de Janeiro as officials have acknowledged they will be unable to fulfill promises to clean up waterways where aquatic sports are to be held. An Associated Press investigation last year found Rio's Olympic water venues are rife with sewage, with such high viral levels that experts say they represent a serious health risk to the approximately 1,400 Olympic athletes slated to compete in them.