The incident occurred between Mankapur and Nawabganj railway stations near Chakrasool village at around 1330 hrs, District Magistrate Sukhlal Bharati said.
He said 13 train passengers and the driver of the truck, which was carrying sand, were killed in the accident that happened at an unmanned crossing.
Eleven, including the truck driver, died instantly while three succumbed on way to hospital, the DM said, adding those sitting on the roof and hanging on doors of the Ayodhya-bound train were also killed.
He said the injured were admitted to various hospitals in Faizabad and Ayodhya where condition of some of them was stated to be serious. The train was packed as most of the passengers were going to Ayodhya to attend Purnima Fair beginning on Monday.
The Railways had announced a compensation of Rs 5 lakh to each bereaved family and Rs 1 lakh to each seriously injured. Those with minor injuries would be paid Rs 10,000 each, a Railway official said. Senior railway officials and a medical team had already reached the scene, he said.