Japanese Prime Minister Shinzo Abe said Monday he had undergone more medical tests but declined to provide details, a week after a first hospital visit that fueled growing speculation about his health.

Government sources close to the prime minister told local media that Abe had returned to the Keio University Hospital to receive the results of the medical checks conducted during the more than seven-hour regular checkup a week prior. 

Abe's admission to hospital on August 17 came a day after former economy minister Akira Amari told a TV program that the prime minister needs to rest, intimating he may be suffering from exhaustion. 

During his first tenure as prime minister, which started in late September 2006, the 65-year-old abruptly stepped down from his post in 2007 due to chronic ulcerative colitis, an intestinal disease. 

Abe returned to office in 2012 with promises to revive the economy and bolster defense. He became Japan's longest-serving prime minister last November. Abe broke another record on Monday after being in power for 2,799 uninterrupted days. The record was previously held by his great uncle Eisaku Sato. 

Under criticism for his handling of the COVID-19 outbreak, Abe has suffered a slide in voter support to one of the lowest levels in his second term.

"I'd like to take care of my health and do my best at my job," Abe told reporters at his official residence after visiting the hospital on Monday. 

His office did not give a detailed explanation for the hospital visits, but close aide Health Minister Katsunobu Kato said last week's visit was a regular check-up and he was "not at all" worried about Abe's health. 

(With input from agencies)