Video report by ITV News Europe Editor James Mates
Donald Trump pressed Vladimir Putin on claimed Russian meddling in the US presidential election in what proved a lengthy first face-to-face meeting at the G20 in Germany.
Rex Tillerson, the US Secretary of State, said the US president raised concerns in a "robust" exchange with the Russian leader during their much-anticipated sideline sit-down.
Mr Tillerson said Mr Putin denied the claims, which are the subject of politically charged investigations in Washington.
Russian foreign minister Sergey Lavrov later said Mr Trump accepted Mr Putin's claim Russia did not meddle in the 2016 vote as the leaders seized the opportunity to discuss global matters at length.
The planned 35 minute chat instead stretched to over two and hours, which included plans for a ceasefire in Syria.
Russia's support for president Assad in Syria was among a number of thorny topics, along with US-opposed Russian interventions in Ukraine.
Both leaders appeared relaxed as they were photographed shaking hands in some of their first contacts in person.
However they seemed more tense in a short press conference for their first one-on-one meeting later in the day.
Donald Trump said he was expecting "a lot of very positive things" in a press conference around their one-on-one talks.
Mr Tillerson later said the leaders agreed to continue discussions over concerns about Russian interference in the US - but were also trying to avoid making it a dominating theme of the bilateral relationship.
"I think the president is rightly focused on how do we move forward from something that may be an intractable disagreement at this point," he said.
Mr Putin was less effusive in his remarks, saying he welcomed the opportunity to talk face-to-face.
"I'm very delighted to be able to meet you personally, Mr President, and I hope as you have said our meeting will yield positive results," he added.
Mr Trump was under intense scrutiny over how he handled the sit-down with the Russian president, a former intelligence agent known to come to meetings well-prepared.
The summit also saw Mr Trump finally meet the Mexican president, Enrique Pena Nieto, for the first time.
The relationship between the leaders has been strained by the US President's pledge to build a wall on the border between their two countries.
The British President Theresa May also met the Chinese president Xi Jinping at the G20.
She is expected to press Mr Xi to do more to stop North Korea's missile testing programme during the weekend summit.
Elsewhere at G20 Mrs May set out her intention to make counter-terrorism a priority on the agenda.
Speaking before meeting other world leaders, Mrs May insisted Britain's intentional role would not be affected after the UK leaves the European Union.
"What I see when I talk to leaders around the world is a genuine interest in working with Britain in the future. A Britain that will be outside the European Union."
Ahead of the talks, the 20 leaders, including host German Chancellor Angela Merkel and French president Emmanuel Macron, gathered for the traditional 'family portrait'.
Riot police clashed with anti-captialist demonstrators in Hamburg for a second day as anti-globalisation activists set dozens of cars on fire.
Protesters also tried to block leaders' delegations from entering the grounds of the Group of 20 summit.