US President George W Bush and Russian leader Vladimir Putin have begun a two-day summit, with divisions over Iran's nuclear programme looming large.
The two leaders greeted each other with a hug and handshake
Mr Bush is expected to call for Russia to suspend nuclear co-operation with Iran, which US accuses of seeking to develop nuclear weapons.
But correspondents say the two men are keen to revive the warm partnership they forged after the 11 September attacks on the US.
Other issues up for discussion at the summit at Camp David, near Washington, are likely to include efforts to bring peace to the Middle East, the reconstruction of Iraq and Russia's ongoing conflict with Chechnya.
The meeting between the two presidents - whose last talks were in June in St Petersburg - began on Friday evening.
President Putin was greeted warmly with a hug and a handshake by Mr Bush.
The two posed for photographs before going off in a golf cart to the closely-guarded cabin where the Russian president will be staying.
Russia has so far turned down American requests to stop helping Iran's nuclear programme.
The International Atomic Energy Agency, urged by Washington, has raised concerns about Iran's nuclear aims and given Tehran until the end of October to dispel fears that it is secretly developing nuclear arms.
President Putin has not silenced all his critics
Russia is building Iran's first nuclear power station, at the southern port of Bushehr - including supplying uranium over a 10-year period from 2005.
American officials say efforts to contain North Korea's nuclear programme will also be discussed.
The US president is also expected to appeal for Moscow's help on forming a new UN resolution on sharing the burden of the reconstruction of and keeping the peace in Iraq.
President Putin opposed the war in Iraq and has expressed his concern at the worsening situation in the Gulf state.
But after recent talks in St Petersburg, both leaders were in agreement that the Iraq crisis strengthened their partnership despite disagreements over the war.
There are also expected to be differences on Russian actions in Chechnya.
Deputy Assistant Secretary of State Steven Pifer warned last week that Moscow's ongoing military campaign against Chechen separatists was among the most troubling issues facing the Camp David talks.
President Putin accused the United States of holding secret talks with Chechen rebel representatives, at a meeting with American journalists.
The last time the two men met, Mr Bush described the Russian leader as honest and straightforward.
But advertisements paid for by Mr Putin's Russian political rivals have appeared this week in American newspapers challenging that perception.
They say Mr Putin has "hoodwinked the West into seeing him as liberal while he flattens democracy and authorises war crimes in Chechnya".
Closer trade ties could also be on the agenda as President Putin told US business executives in New York on Friday that Russia wanted to be supplying America with 10% of its oil exports within seven years and was looking at the infrastructure developments that would be needed.