By Hai Yang, Yu Maofeng and Lu Jingli

US President Barack Obama's left Moscow on Wednesday, concluding his visit to Russia which was described as as effort to "reset" the strained relations between the two countries.

Several vital agreements including a framework document for a new strategic arms reduction treaty were inked on the first day of Obama's visit, marking a gradual thawing of bilateral ties.

However, local media and observers anticipate a long, difficult road ahead for the two countries on their way to improve relations.

Vital deals reached

After their first face-to-face meeting in London early this April, Medvedev and Obama pledged to "reset" their strained relations. The replacement of the Strategic Arms Reduction Treaty (START I) that is due to expire on December 5 is widely regarded as the breakthrough for such a "reset" process.

After three rounds of talks behind closed doors before the presidents met, the two leaders finally inked a document of understanding on nuclear weapon control on the first day of their Moscow summit.

Under the framework document adopted by the two presidents, within seven years after a new treaty comes into force, the number of strategic delivery systems should be limited to between 500 to 1,100 units and warheads to between 1,500 to 1,675 units. The two countries should only deploy strategic offensive weapons within their domestic territories.

"This legally binding treaty will be completed by the end of this year," Obama said. He expressed the hope that the two countries would reduce their nuclear arms by as many as one third and move even beyond that in subsequent treaties.

After five hours of talks, Medvedev and Obama also signed a joint statement on missile defense.

Russia and the US plan to continue talks on cooperation regarding issues such as anti-missiles and non-proliferation of ballistic missiles, according to a statement from the Russian foreign ministry.

On a basis of mutual respect for security interests, it said, both sides will actively seek the best way to strengthen reciprocal strategic relations.

The summit also saw an agreement allowing 4,500 flights a year carrying US troops and weapons to Afghanistan across the Russian territory for free. Obama hailed this move as a "substantial contribution by Russia to an international effort," as it will save the US troops time and money.

The two leaders vowed to cooperate on the fight against terrorism, extremism and drug trafficking in Afghanistan.

The two leaders also agreed to set up a joint presidential commission to expand cooperation on nuclear safety, arms control, counter-terrorism, as well as cooperation in trade and economy, science and technology, education and cultural exchanges.