Bill Browder has described himself as "Putin's No 1 enemy". Now the Russian president had added weight to that claim by singling out the British investor at his controversial summit with Donald Trump on Monday.

The UK-based financier appeared to be part of what the US president called an "incredible offer" by Vladimir Putin to assist American investigators in their prosecution of 12 Russian intelligence officers accused of hacking crimes during the 2016 presidential election season.

"He offered to have the people working on the case come and work with their investigators with respect to the 12 people," Mr Trump told reporters during a news conference in Helsinki following his joint summit with Mr Putin.

The special counsel investigating potential coordination between the Trump campaign and the Kremlin charged a dozen Russian military intelligence officers on Friday with hacking the Democratic National Committee and the Hillary Clinton campaign and then releasing the stolen communications online as part of a sweeping conspiracy to meddle in the election.

While Mr Trump did not elaborate on the Russian leader's "incredible offer," Mr Putin himself suggested that special counsel Robert Mueller could ask Russian law enforcement agencies to interrogate the suspects. He said US officials could request to be present at such questioning in line with a 1999 agreement on mutual legal assistance in criminal cases.