LONDON—Russia edged closer to a potential default on its international debt on Wednesday as it paid dollar bondholders in roubles and said it would continue to do so as long as its foreign exchange reserves are blocked by sanctions. The United States on Monday stopped Russia from paying holders of its sovereign debt more than $600 million from reserves held at U.S. banks, saying Moscow had to choose between draining its dollar reserves and default. Russia has not defaulted on its external debt since reneging on payments due after the 1917 Bolshevik Revolution. “This speeds up the timeline around when Russia runs out of space on willingness and ability to pay,” one fund manager holding one of the bonds due for payment on Monday said. The Kremlin said it would continue to pay its dues. “Russia has all necessary resources to service its debts … If this blockade continues and …