
He said Medvedev understands that, but Putin needs convincing that the U.S. wants cooperation rather than "an antagonistic relationship."
On Afghanistan, Obama said he intends to reassess the possible need for additional U.S. troops after the nation holds national elections in August, but that he believes America's key goals can be met there "without us increasing our troop levels."
He has ordered 21,000 more troops to Afghanistan this summer, bringing the U.S. total to 68,000. He spoke on a day when 4,000 of those newly arrived Marines stormed through southern Afghanistan and when news surfaced that an American soldier who disappeared after walking off his base in eastern Afghanistan was believed captured.
Obama outlined his benchmarks for making any new decision about troops there: whether al-Qaida and other terrorist groups can set up safe havens in Afghanistan, whether the Afghan national army and police can secure the country without assistance, and whether the border with Pakistan can be made less porous.
"We can't tolerate a situation in which terrorist organizations act with impunity," he said.
Minutes before his vice president, Joe Biden, landed in Iraq for a two-day visit, Obama said he was confident — but not certain — that the timetables for removing U.S. troops from that war will hold. This week marked a major milestone in the war when U.S. troops pulled out of major Iraqi cities.
"I reserve the right to make changes based on changing circumstances to protect U.S. security," he said.
As for Guantanamo detainees, the former constitutional law teacher expressed doubts about his call to create a new legal framework to deal with terror suspects considered too dangerous to release but also impossible to prosecute, a potential major change in American jurisprudence.
"We're going to proceed very carefully on this front, and it may turn out that after looking at all the dimensions of this that I don't feel comfortable with the proposals," Obama said. "We don't have a tradition of detaining people without trial."
He added: "How we deal with those situations is going to be one of the biggest challenges of my administration."