International aid agency Mercy Corps has suspended its operations in two states in north-eastern Nigeria affected by the Boko Haram insurgency.
The decision to stop work in Borno and Yobe comes after the army closed four of its offices, without explanation, in the region, Mercy Corps said.
According to the website Sahara Reporters, the offices were shut down after the army found $94,000 (£76,200) of cash being transported in a Mercy Corps vehicle. It is not clear what the concern was about the money.
The development comes days after the army stopped the work of non-governmental organisation Action Against Hunger, accusing it of supplying Islamist militants with food and drugs.
On Wednesday, the NGO said one of six hostages, who included one of its employees, two drivers and three health ministry personnel, being held by militants since July had been killed.
The group urgently called for the release of five other hostages.
Thousands of people affected by the violence in the region rely on aid organisations for assistance.