The international community has "made a mistake" with the intensity of its focus on the global HIV-Aids epidemic and lost ground on family planning issues as a result, according to the head of the United Nations population agency.

In an interview with the Guardian as the world population reaches seven billion, Babatunde Osotimehin, the executive director of the UN Population Fund, said efforts to expand family planning services in the developing world stalled for a decade while global health organisations turned their energies to fighting HIV-Aids.

"We made a mistake. We disconnected HIV from reproductive health. We should never have done that because it is part and parcel," he said.

About 60 million people have been infected with or died from HIV-Aids in the 30 years since the virus was first identified in the US. Meanwhile, the global population is due to hit seven billion on 31 October. About 1.8 billion are young people, the vast majority of whom are living in the world's poorest countries.

By criticising decades of development policy by the UN and world governments, Osotimehin's remarks are hugely controversial. Experts on HIV-Aids and population challenged his views.

"I find it difficult to understand how any development leader can believe that funding for Aids in Africa was a distraction from other priorities. Aids was, and continues to be, a make-or-break emergency in much of sub-Saharan Africa," said Siddharth Dube, a former senior adviser at UNAids and a senior fellow at the World Policy Institute in New York.

Erika Larson, an international policy advocate for Population Action International, said: "There is no doubt that the incredible investment in a rapid response to address the HIV/Aids crisis has saved many lives."

Osotimehin, a doctor and former health minister in Nigeria who is the father of five children, suggested HIV-Aids was a bigger setback than the policies of George Bush – who cut funding to the UNPF and other family planning efforts. He said family planning was already "off the radar" at the time because of the preoccupation with HIV-Aids.

"A lot of us that were trained and had skills in reproductive health moved to HIV and the world believed at the time that HIV … could be solved as an emergency. You could wipe it off and come back to business as usual," he said.

He had found it difficult to talk about family planning at the height of the HIV-Aids crisis. "It was going to be impossible for me to stand up in a country where young men and women are dying and to say 'Excuse me I think you need to cut down on birth rates'. It was just not kosher," he said. "You couldn't begin to tell people 'You know, you are still having too many children,' when they had just lost their kids."

The international community was not working to integrate its programmes on HIV-Aids and family planning, said Larson. But it was a challenge.

"Often times, the HIV and reproductive health communities were pitted against each other, but it was the woman who had to visit three different clinics to get what she needed," she said. "Family planning has a role in fighting the HIV-Aids epidemic, especially in preventing unwanted pregnancy among HIV-positive women and reducing mother-to-child transmission. Family planning should be available to all women, regardless of HIV status."

Osotimehin said the international community was regaining momentum in its efforts to make family planning services available to women in all countries.

He rejected setting a population target and did not attach much importance to the symbolic value of world leaders limiting their own family size. Instead, he viewed family planning as an integrated part of development. "It's not just about population. It's also about consumption," he said.

He argued it was crucial for developing countries to devote a larger share of their own resources to family planning and health.

The 20 countries projected to have the fastest population growth are the poorest in the world, but Osotimehin argued that they could not continue to rely on development assistance for health and family planning programmes.

"A country must take ownership of the welfare of its people at some point," he said.