In her last address to the security council, the UN human rights chief has sharply criticised the body for its ineffectiveness on Syria and other intractable conflicts, saying its members have often put national interests ahead of stopping mass atrocities.

“I firmly believe that greater responsiveness by this council would have saved hundreds of thousands of lives,” said Navi Pillay, whose term as high commissioner for human rights ends on 30 August.

Pillay said Syria’s conflict “is metastasing outwards in an uncontrollable process whose eventual limits we cannot predict”. She also cited conflicts in Afghanistan, the Central African Republic, Congo, Iraq, Libya, Mali, Somalia, South Sudan, Sudan, Ukraine and Gaza.

“These crises hammer home the full cost of the international community’s failure to prevent conflict,” Pillay said. “None of these crises erupted without warning.”

Pillay spoke at a meeting where the security council unanimously adopted a resolution promising more aggressive efforts to prevent conflicts.

The resolution acknowledged that the United Nations has not always used the tools in its charter for preventing conflict. It prescribed several steps for improvement, focusing on addressing human rights violations earlier and recognizing that such abuses are often warning signs of looming conflicts.

The resolution encourages the secretary general to bring any matter that he believes threatens international peace to the attention of the security council and promises to promptly consider those cases.

The resolution said little about the political differences that often paralyze the security council, where sharp divisions between veto-holding members Russia and the United States have often thwarted action on Syria and Ukraine.

Pillay touched on the problem in her remarks. “Short-term geopolitical considerations and national interest, narrowly defined, have repeatedly taken precedence over intolerable human suffering and grave breaches of and long-term threats to international peace and security,” she said.

The human rights chief said the use of veto power on the security council “to stop action intended to prevent or defuse conflict is a short-term and ultimately counter-productive tactic”.

Pillay offered her own solutions. She proposed that the council adopt a menu of new responses, including “rapid, flexible and resource-efficient human rights monitoring missions”. And she suggested building on the Arms Trade Treaty by requiring that, in countries where there are human rights concerns, governments accept a small human rights monitoring team as a condition of purchasing weapons.

In his own address to the council the UN secretary general, Ban Ki-moon, was milder but said “it is the time for a new era of collaboration, cooperation and action from the Security Council.”

He cited the consensus on removing chemical weapons from Syria as a success case for the Security Council. But he said when “our actions come late and address only the lowest common denominator, the consequences can be measured in terrible loss of life, grave human suffering and tremendous loss of credibility of this council and our institution.”