The head of the humanitarian body’s delegation in Nigeria, Zoran Jovanovic, said the problem was worst in the northeast, which has borne the brunt of Boko Haram violence and the military response.
“The availability of shelter, food, water, clothes and health services has worsened in that region,” he said in an emailed statement.
According to the United Nations, as of last month nearly 12,500 Nigerians had fled east to neighbouring Cameroon and 8,000 north to Niger because of the continued violence.
The ICRC said it had been helping those who have stayed and since August last year, more than 18,000 people in Borno state had been given shelter and essentials.
About 45 percent of them were women, including many widowed and elderly, it added.
Assistance also included daily food rations, given that prices have rocketed because of the conflict and there are frequent shortages of essential items.
The Boko Haram insurgency, which began in 2009, is the country’s most pressing security issue and last year saw three northeast states placed under emergency rule.
The Council on Foreign Relations this week said that 3,383 people had died in Boko Haram attacks since May 2011 when President Goodluck Jonathan took office.
The US thinktank said it uses the start of Jonathan’s presidency because “it was an event that highlighted the increasing bifurcation of the country on regional and religious lines”.
The ICRC, meanwhile said it had for the first time been granted access to people held in custody in military-run facilities in Borno.
The visits took place last month but no further details would be issued, it added.
Rights groups have criticised not only the mass detention of ordinary Nigerians suspected of Boko Haram links but also the conditions in which they were being held.
Human Rights Watch said in November last year that there were “credible” claims of torture and deaths in custody.