Oleg Deripaska, a Russian oligarch once close to President Donald Trump's former campaign manager, has offered to cooperate with congressional committees investigating Russian meddling in the 2016 election, but lawmakers are unwilling to accept his conditions, according to congressional officials.

Deripaska's offer comes amid increased attention to his ties to Paul Manafort, who is one of several Trump associates under FBI scrutiny for possible collusion with Russia during the presidential campaign.

The two men did business together in the mid-2000s, when Manafort, a Republican operative, was also providing campaign advice to Kremlin-backed politicians in Ukraine. Their relationship subsequently soured and devolved into a lawsuit.

Deripaska, an aluminum magnate who is a member of the inner circle of the Russian president, Vladimir Putin, recently offered to cooperate with congressional intelligence committees in exchange for a grant of full immunity, according to three congressional officials.