A bomb exploded Thursday at the mausoleum of a 17th century Sufi poet in northwestern Pakistan, underscoring the gulf between hard-line Muslims and those in the region who follow a traditional, mystical brand of Islam.

A letter delivered three days before the attack to the management of the mausoleum of Sufi poet Rehman Baba on the outskirts of Peshawar warned against its promotion of "shrine culture," said Sahibzada Mohammad Anees, a top government official in the city.

The letter also noted that women were coming to pray at the shrine, he said.

The blast damaged one corner of the shrine, but no one was injured.

Many Pakistanis like to pray at the tombs of mystics and holy men — a practice opposed by hard-line Muslims as un-Islamic. The extremists also believe Islam prohibits men and women from mingling unless they are husband and wife or close relatives.

"To try to destroy his tomb is a heinous thing," said Shah Hussein, a visitor to the shrine. "It is a very great shame."

Baba's poems were laced with Islamic mysticism or Sufism and remain popular among the Pashtun people of northwest Pakistan and Afghanistan. A professor at Peshawar University told a local TV station that in many Pashtun homes, Baba's poems are kept alongside the Islamic holy book, the Quran.

Islamist militants have increased their hold over much of northwest Pakistan in recent years and are increasingly seen as a threat to other areas of this nation of 170 million people.