With John Kerry and Sergei Lavrov set to continue their discussions on the Syria crisis, a former British diplomat who spent many hours across the negotiating table from the Russian Foreign Minister says the US is "taking on the master".
Carne Ross was a diplomat at the UN Security Council between 1998 and 2002. In that time he negotiated on issues, including the Arab-Israeli conflict, Afghanistan, and spent an "awful lot of time" with Lavrov - the then Russian Ambassador to the UN - negotiating weapons inspections in Iraq.
Describing his dealings with the Russian Foreign Minister, Mr Ross said: "He was extremely professional, extremely competent and in my view, the most brilliant negotiator with the Security Council at that time."
"When he chooses to be obstructive, he can be very obstructive. On disarmament he is extremely knowledgeable and aware of every minute detail of how disarmament is organised," he added.
US Secretary of State John Kerry has said talks with Lavrov over Syria's chemical weapons have, so far, been constructive. The pair are set to meet again at the end of the month.
As the attempts at diplomacy continue, Mr Ross says Lavrov is likely to play a vital part in proceedings.
"He will have an extremely big role - this is what he knows," he said.
"He is a highly engaged foreign minister and he knows the UN Security Council backwards.This is a problem for the US, as John Kerry has never done that. They are up against it. They are taking on the master."
"He is a professional, he doesn't scream and shout. He is there to get business done," he added.
Mr Ross, who now runs the world's first non-profit diplomatic advisory group - Independent Diplomat - and is currently working with the Syrian Coalition, believes many months of talks lay ahead for Russia and the US, meanwhile "Assad is killing his own people every day".
"The United States is walking into a trap they will be talking together for months," Mr Ross said.
"I have been in this situation. I spent a whole year of my life negotiating a resolution on terms of Iraq weapons inspections."
The former British diplomat describes chemical weapons as the "crown jewels" of the Assad regime, which are used to "threaten the rebels, but also to deter the Israelis and anybody else. They are a strategic terror weapon."
Mr Ross explains the US have not had a "clear, distinctive strategy" on Syria and believes they did not enter the crisis wanting chemical weapons disarmament.
Meanwhile, Russia's aims are clear, Mr Ross says.
"[Russia] think the Assad regime should be maintained and they have influence there," he said. "They are also worried about the consequences of extremists getting into power in Syria. They also don't think Assad is going to give up and they are not going to force him to do so."