Nearly three quarters of all millennials in 15 countries believe mental health needs are as important as water, food and shelter for victims of wars and armed violence, according to a survey commissioned by the International Committee of the Red Cross (ICRC).

The survey, released ahead of World Mental Health Day, which falls on Thursday this year, covered more than 15,000 people aged 20 to 35 in countries including Afghanistan, Syria, Palestine, Russia and the United States.

Of the 15 countries surveyed, the highest support for mental health among millennials came from Syria, where 87 percent of roughly 1,000 respondents said mental health needs are as important as water, food and shelter for victims of armed conflicts. The next highest countries were Indonesia (82 percent), Ukraine (81 percent) and Switzerland (80 percent), according to ICRC. The average rate was 73 percent.

In a statement, the ICRC called on all countries to prioritize mental health and psychosocial support in situations of violence and armed conflict.

"Mental health services have for too long been an after-thought in conflict settings. When traumas are invisible, they can be easily overlooked or deprioritized. Yet war has a devastating impact on the mental health and psychosocial well-being of millions. New mental health problems can appear, and pre-existing conditions may resurface. For some the effects will be life-threatening," said ICRC President Peter Maurer.

"Supporting people's mental health can be lifesaving in times of war and violence, just as much as stemming a bleeding wound or having clean water. Hidden wounds are no less dangerous," said Maurer.

More than one out of five people in conflict-affected areas live with some form of mental health condition, from mild depression and anxiety to post-traumatic stress disorder. That is three times more than the general population worldwide suffering from these conditions, according to ICRC.