South Korea's spy agency says North Korea appears to have sent more troops to Russia, after its soldiers deployed on the Russian-Ukraine fronts suffered heavy casualties.

Finance ministers and central bankers from the G20 top economies gather in South Africa on Wednesday and Thursday, for a meeting marred by the absence or curtailed attendance of key members and disputes over the main issues of climate, debt and inequality.

Ukrainian troops holding positions in Kursk say the North Koreans have reappeared on the battlefield and become even more formidable foes.