Coach Juergen Klinsmann said South Korea are still going through a transition period and wants to see his squad build a strong mentality as they head toward next year's Asian Cup in Qatar.

The Koreans extended their winless run under the German to five games on Thursday with a 0-0 draw against Wales.

Klinsmann, 59, was appointed in February and tasked with building on South Korea's run to the knockout rounds of last year's World Cup. Prior to Thursday's game they had drawn against Colombia and El Salvador and lost to Uruguay and Peru.

"The team is in the process of developing toward Qatar," Klinsmann told reporters in Cardiff. "It's a normal process between two World Cups that there's a type of a turnover into the next generation of players.

"For me, it's very important to see where they are mentally ... and I look a lot about how the team develops as a group. If you want to win or want to go far in a tournament, you need a very, very strong spirit."

Captain Son Heung-min also came to Klinsmann's defence after the German was criticised for spending more time at his US home than in South Korea since his appointment.

"I understand where fans come from, as someone who's been on the national team for a long time," Son said. "I am not saying the coach is always right, but I also don't think fans are always right, either.

"Many different players have been getting opportunities. In some ways, the coach is trying to identify new players, instead of trying to put up results right away. I am sure he knows what he's doing."