MEXICO CITY: Mexico needs to produce results in cases like the 43 missing students and alleged incidents of extra-judicial killings to show its commitment to human rights, the US ambassador to the United Nations said Thursday. Ambassador Samantha Power said 'the will is there,' after three days of meetings with top law enforcement and citizen's groups around crime, violence and judicial reform in Mexico. But she said it's important that words be followed with concrete results to show both Mexicans and the world that the government is serious about eliminating abuses and improving the rule of law. Power, who spoke in the northern city of Monterrey, referred specifically to the case of the 43 teacher college students who disappeared at the hands of local police more than a year ago in the city of Iguala in the southern state of Guerrero. The attorney general's version that they were killed and burned in a giant pyre was taken apart by an independent group of international experts. She was also asked about two incidents of possible extra-judicial killings by federal police and said progress on those cases, as well as those of missing persons and torture in custody, would show the country is undergoing change. 'It's impossible to fix the whole system overnight,' Power said. 'But if progress could be made in the Iguala case, or if progress could be made on the cases you raise ... and resources are dedicated and accountability is achieved, that sends a really important signal.' International human rights groups have urged Mexico to investigate possible extra-judicial killings of more than 50 people by federal police in separate incidents this year. So far Mexico has refused. The United States earlier this month withheld $5 million in anti-drug aid to Mexico over concerns about human rights in the country. It's a small portion of what the US gives Mexico each year but conveys a pointed message to its southern neighbor. The US has given Mexico $2.4 billion since 2008 to fight drug-trafficking and strengthen its judicial system. Power said there are no specific criteria for restoring the money, rather an overall assessment that Mexico meets US criteria on human rights for foreign governments receiving aid.