Lisbon, Portugal (CNN) -- Russia and NATO, once wary and untrusting of each other, have decided to deepen their ties, with both agreeing Saturday to work closely on the crucial issue of missile defense.
President Barack Obama and NATO Secretary-General Anders Fogh Rasmussen also said both entities will step up cooperation across the board, including Russia's agreement to allow non-lethal NATO supplies to and from its territory for the war effort in Afghanistan.
"We see Russia as a partner, not an adversary," Obama said while attending the NATO summit in Lisbon.
Russian President Dmitry Medvedev, also in Lisbon, agreed to begin working on missile defense cooperation, and the two sides will exchange information and work with each other to defend themselves.
Medvedev, while noting there are still disagreements such as the issue over the Republic of Georgia, reiterated the point that NATO and Russia are bolstering cooperation.
"The NATO Russia summit is a very important step in the reinforcement of our relationship," he said.
NATO Secretary-General Anders Fogh Rasmussen said that "today we launch a fundamentally new phase in relations between NATO nations and Russia. Today, we help not only bury the ghosts of the past that have haunted us for too long, we exorcise them. Today, we make a fresh start."
NATO said in a declaration Saturday that it is "determined to build a lasting and inclusive peace, together with Russia."
"We need to share responsibility in facing up to common challenges, jointly identified. We want to see a true strategic partnership between NATO and Russia, and we will act accordingly, with the expectation of reciprocity from Russia," it said.
Noting that NATO-Russia cooperation has improved over the last year, NATO identified several facets of cooperation.
They include counternarcotics; non-proliferation of weapons of mass destruction and their means of delivery; counterpiracy; counterterrorism; and disaster response.
"We also welcome the new extended arrangements offered by Russia to facilitate ISAF transit to and from Afghanistan," the declaration said. "We are actively pursuing cooperation with Russia on missile defense, including through the resumption of theatre missile defence exercises."
In the NATO-Russia Council, the alliance also wants to deal with topics such as "military deployments, including any that could be perceived as threatening; information sharing and transparency on military doctrine and posture, as well as the overall disparity in short-range nuclear weapons; arms control; and other security issues. "
"We look forward to discussing all these matters in the NRC, which is a forum for political dialogue at all times and on all issues, including where we disagree," NATO said. "Our dialogue and cooperation with Russia also help us to resolve differences by building trust, mutual confidence, transparency, predictability and mutual understanding."
Meanwhile, the START treaty, the proposed nuclear pact between the United States and Russia, emerged as a major topic in Lisbon.
Obama has called ratification of the treaty -- which would restart mutual inspections, while limiting both nations to 1,550 warheads and 700 launchers each -- a priority during Congress' lame-duck session, saying it's critical to national security and a cornerstone of U.S.-Russia relations.
But 10 GOP senators, led by Sen. Jon Kyl of Arizona, have urged a delay until the next Congress over concerns about the current congressional workload and over-modernization of the U.S. nuclear arsenal.
Obama emphasized the need for the treaty to be adopted. He told reporters that Kyl wants a "safe and secure America just like I do" and never said to him that Kyl's opposed to the treaty.
But Obama said he has received "overwhelming support from our allies here that the new START treaty is a critical component" to U.S. and international security.
He said generals from previous administrations back the treaty and said the issue has gone through many hearings, meeting concerns over modernization.
"It's time for us to go ahead and get it done," he said.
Rasmussen said a delayed ratification "will be damaging to the overall security environment in Europe."
"We strongly urge both parties to ratify the START treaty as early as possible," he said.
Obama also said Russia has provided "enormous help" in dealing with Iran's nuclear program.
"It would be a profound mistake to slip back into mistrust as a consequence of a failure to ratify," he said.
CNN's Elise Labott contributed to this report.