US President Barack Obama said Thursday he was "very concerned" about extremists on the border between Pakistan and India and urged a cooling of cross-border tensions with an "effective dialogue". Obama told reporters after talks with Indian Prime Minister Manmohan Singh on the sidelines of the G20 economic summit that they had discussed the threat posed by the militants on the frontier of the nuclear-armed neighbour states. Asked by an Indian journalist of his assessment of the danger posed by extremists coming into India from Pakistan, Obama said: "Obviously we are very concerned about extremists and terrorists who have made camp in the border regions of Pakistan as well as in Afghanistan. "But we spoke about it more broadly, in terms of how we can coordinate effectively on issues of counter-terrorism." Obama said that India and Pakistan had more mortal enemies than each other. "At a time when perhaps the greatest enemy of both India and Pakistan should be poverty... it may make sense to create a more effective dialogue between India and Pakistan," he said. The president also praised Singh's leadership, saying he was "a very wise and decent man, and has done a wonderful job in guiding India, even prior to being prime minister, along a path of extraordinary economic growth". Singh told a separate news conference that he and Obama had agreed to join forces to fight terrorism. "We both agreed that our two countries must work together to counter the forces of terror," he said, adding that they had a "global strategic partnership". "We both have agreed that there are enormous opportunities to further strengthen our relationship to make this partnership more productive, more durable and diverse," he said. Singh added, however, that the ball was in Pakistan's court over the deadly Mumbai terror attacks last November, pressing Islamabad to "convince us that it is sincere" about tracking down those responsible. Questioned about Pakistan's response to the bloodbath, he said: "We expect Pakistan to do all that is required to bring the culprits of the Mumbai terror attacks to book. "We have supplied Pakistan (with) answers to all the questions that there are. The ball is in the court of Pakistan. It has to convince us that it is sincere about bringing to book the culprits of Mumbai."