As Moscow and Washington hailed co-operation to help end Syria's civil war, troops backed by Russian air support fought their way into the Islamic State-held city of Palmyra.
US Secretary of State John Kerry met President Vladimir Putin in Moscow in an atmosphere that was noticeably more amiable than past meetings.
Putin, who has announced he is winding down Russia's military involvement in Syria, offered warm words for President Barack Obama, a sign relations are improving after Washington imposed sanctions on Russia over its intervention in Ukraine in 2014.
"We understand that what we have been able to achieve on Syria has been possible only thanks to the position of the US top political leadership, President Obama," Putin said at his meeting with Kerry.
"I very much hope that your visit will allow us to bring our positions closer on moving forward to solve the Syrian crisis and ... on Ukraine."
Moscow is the main ally of President Bashar al-Assad's government, while Western countries back those trying to overthrow him during five years of civil war that has killed 250,000 people and led to the world's worst refugee crisis.
Both superpowers share a common enemy in Islamic State, the Sunni Muslim fighters who have declared a caliphate to rule over all Muslims from territory in Syria and Iraq.
After Russia intervened with air strikes to shore up Assad last year, Washington and Moscow jointly sponsored a peace process that has produced the first sustained ceasefire and negotiations involving the warring parties.
The ceasefire does not cover Islamic State, allowing Damascus to ramp up its fight against the jihadists.
After the West accused Moscow of helping Assad fight mainly other foes, Damascus launched a major offensive this month to take back Palmyra.
The British-based Syrian Observatory for Human Rights said the army had advanced into the hotel district just to the southwest of the city and reached a residential area, after a rapid advance the day before brought the army and its allies right up to its outskirts.
In Geneva, the peace talks involving Assad's government and his foes which began this month are expected to adjourn until April.
The two sides expected to agree to a document drawn up by UN envoy Staffan de Mistura outlining basic principles, in what one diplomat called a "baby step" forward.
A summary of the document seen by Reuters includes reforming state institutions, rejecting terrorism unequivocally and implementing United Nations Security Council resolution 2254 that guarantees a political transition of power.
It also calls for no tolerance of acts of revenge from either side, rebuilding the Syrian army on national criteria, ensuring a democratic non-sectarian state and preserving women's rights in fair representation.
The sides still have yet to address the biggest challenge: the nature of a post-war "political transition".
Opposition leaders say Assad must leave power; the government says this is not up for negotiation.
Washington believes that Moscow can nudge Damascus to make concessions.
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