Villagers carry what's left from their collapsed houses after heavy flooding in Dera Ismail Khan, Pakistan, on Sunday. (Ishtiaq Mahsud/Associated Press)

The number of people killed in flooding in northwest Pakistan has risen to more than 1,100, officials said Sunday.

Monsoon rains caused the worst floods on record in Khyber-Pakhtoonkhwa province in the past week, washing away villages, roads and bridges.

Pakistani army spokesman Maj.-Gen. Attar Abbas said the full scale of the devastation is still not clear and the death toll is expected to increase.

"Aerial monitoring is being conducted and it has shown that whole villages have washed away, animals have drowned and grain storages have washed away," said Latifur Rehman, spokesman for the Provincial Disaster Management Authority. "The destruction is massive."

The UN estimates about one million people are affected by the flooding, while 27,000 remain trapped by the water.

Almost 700 people have drowned in the Peshawar valley, which includes the districts of Nowshera and Charsada, and 115 others are still missing, a local official said.

The districts of Swat and Shangla have also been hit hard and have suffered more than 400 deaths, said Mujahid Khan, the head of rescue services for the Edhi Foundation, a private charity.

Residents of Swat were still trying to recover from a major battle between the army and the Taliban last spring that caused widespread destruction and drove some two million people from their homes. About one million of those were still displaced.

In Swat alone, the floods have destroyed more than 14,600 houses and 22 schools.

With files from The Associated Press