BRUSSELS - NATO chief Jens Stoltenberg sidestepped questions on Friday about U.S. President Joe Biden's health ahead of an alliance summit in Washington next week, saying one reason for NATO's success was that it stayed out of domestic political issues.

Biden's health has become a major issue in the U.S. election campaign following his shaky performance in a debate with Republican opponent Donald Trump last week.

Biden will participate in a flurry of events over the next week aimed at showing he still has the stamina to run in the Nov. 5 election.

Asked whether he was worried the focus on Biden's capabilities could overshadow NATO's message at the summit, Stoltenberg said that NATO summits always take place within a domestic political context.

"What NATO can do is focus on the substance of NATO, and that is what we will do," Stoltenberg, the secretary-general, told a pre-summit news conference at NATO headquarters in Brussels.

Asked whether he believed Biden is mentally and physically fit enough to lead NATO's biggest nuclear-armed member in coming years and whether he had noticed any decline in Biden's condition, Stoltenberg said he had met with Biden a couple of weeks ago and had good meetings with him in the Oval Office.

"We made progress in the preparations for the upcoming NATO summit," he said, adding that he welcomes Biden's strong personal leadership on support for Ukraine.

But he said any further comments could be damaging for NATO.

"One of the reasons why NATO is successful is that we have always stayed out of domestic political issues," he said.

"If I start to say anything that makes it possible to connect me to ongoing political debates in any allied country, I will actually weaken the alliance."

  - Reuters