The warning came as florists, hotels and restaurants ramped up promotions for the occasion, offering roses inscribed with sentimental proclamations, idyllic seaside escapes and candlelight dinners with popular singers serenading lovers.
There are no laws banning Wednesday's celebration in either country, which advocate moderate Muslim teachings, but some officials noted that Saint Valentine was a Christian and feared that romantic revelries might prompt impure behavior among young people.
"From the point of view of Islam, this is not an advisable practice," said Muhammad Ramli Nuh, a state lawmaker who belongs to the ruling United Malays National Organization. "Unmarried couples might come together and mingle with each other in unacceptable ways."
"We feel it is inappropriate for businesses to hold Valentine's Day programs for couples," said Muhammad Ramli, deputy chairman of the government's Islamic development council in Malaysia's northeastern Terengganu state.
In neighboring Brunei, spiritual leaders used mosque sermons last Friday to express concerns that couples "might not just send greetings and gifts but ... go beyond the limit and even engage in promiscuous activities."
"It is sad to note that we also celebrate such an occasion without knowing its origin, whether it is permissible in Islamic beliefs or otherwise," the imams said in a message carried by Brunei media. "Valentine's Day is not a celebration needed among Muslims."
Muslims should not "follow Western cultures in the name of modernization without knowing that such culture is against the Islamic teachings," the message added.
But the advice did not deter businesses from capitalizing on Valentine's Day.
One Brunei florist reportedly imported 1,000 roses with phrases such as "Thinking of You" and "You Are Mine" inscribed on their petals.
A beach resort in Terengganu publicized a "Romantic Interlude Package" that includes spa treatments and a tree-planting ceremony to commemorate each couple's stay, the AP reports.
Saint Valentine is believed to have been a 3rd century martyred Roman priest or bishop. Theories of how the holiday became a celebration of lovers include that it stemmed from Valentine's Feb. 14 feast date falling close to a pagan love festival or that it was because mid-February was seen in Europe as the time of year when birds start mating.