Kremlin says Putin didn't set his alarm to tune into Biden-Trump debate

President Vladimir Putin did not get up in the middle of the night to watch the US presidential debate between Joe Biden and Donald Trump, and Russia will not comment on internal US politics, the Kremlin said on Friday.

Putin has professed indifference to the outcome of the November election and his spokesman Dmitry Peskov maintained that line, saying Russia had more important things to focus on.

"Well, look, I don't think you expect the president of Russia might set an alarm clock, wake up before morning and watch the debates in the United States of America?" Peskov told reporters when asked if Putin had tuned in.

"We have a lot of issues that are really important for our country, which are relevant for us. These are the issues that our president is dealing with. Debates in the United States are not part of the main issues on the agenda."

Biden put in a shaky performance in the encounter with Trump, which revived discussion about whether he is too old to seek a second term. Russia loomed large in the debate as both men tried to show who was tougher on foreign policy.

Trump said if the US had a "real president" who was respected by Putin, the Russian leader would never have invaded Ukraine.

Biden responded: "Go ahead, let Putin go in and control Ukraine, and then move on to Poland and other places. See what happens then. He (Trump) has no idea what the hell he's talking about."

The outcome of the election matters to Russia, despite its attempts to play it down, because it will determine the extent of Washington's commitment to keep backing Ukraine against Moscow and supplying it with advanced US weapons.

In a February interview, Putin said he was willing to work with any US president but preferred Biden because he was "a more experienced, predictable person, a politician of the old school".

Some commentators saw that remark as mischief-making. Based on Trump's reluctance to criticise Putin when he was president as well as on his more recent comments - including that he would encourage Russia to attack NATO members that failed to spend enough on their own defence - his critics believe he would give the Kremlin leader an easier ride.

Earlier this month, Putin said in response to a Reuters question that Russia did not care who the next US president was, as this would probably not change anything for Moscow. But he said the U.S. court system was clearly being used in a political battle against Trump.

Some Russian politicians such as former president Dmitry Medvedev have questioned the mental capacity of Biden, who is 81. Putin, a decade younger, has not joined those attacks but has alluded to the discussions over Biden's age.

"When I met with Biden in Switzerland - true, that was several years, three years ago - people were already saying he wasn't up to it. I didn't see anything of the kind," he said in February. Soon afterwards, Biden described Putin as a "crazy SOB".