As diplomacy intensifies on ending the Iran war, top US diplomat Marco Rubio was spending Monday not in negotiations but at India's world-famous monument to love, the Taj Mahal.

Rubio, on his first-ever visit to India, flew to Agra and spent 45 minutes at the Taj Mahal with his wife Jeanette, who usually shuns the spotlight.

"It's one of the wonders of the world," Rubio said of the Taj Mahal.

"I think it's important to show respect to the culture of the countries that you visit."

Under a blazing sun in 40C heat, Rubio removed the tie from his navy-blue suit, put his arm around Jeanette, who wore a flowing dress with elegant heels.

The couple posed for pictures on the bench from where Princess Diana was photographed alone in an iconic 1992 shot.

The US ambassador to India, Sergio Gor, a high-octane former aide to President Donald Trump, smiled and eagerly joined some of the couple's pictures.

The normally teeming street leading to the Taj Mahal were cleared for Rubio, with other tourists kept 100 metres away from him -- although it was only a partial shut down unlike when Vice President JD Vance visited.

Rubio was not entirely away from Iranian influence at the Taj Mahal, whose domes and four-way charbagh gardens are heavily influenced by Persian architecture.

The Taj Mahal was built in the 17th century on orders of Mughal emperor Shah Jahan as a mausoleum for his beloved wife Mumtaz Mahal who died in childbirth.

The excursion is unusual for Rubio, who in nearly a year and a half on the job has preferred short, business-like trips and rarely done events outside of government meetings.

Rubio said he was taking advantage of a one-day break in his schedule before a meeting in New Delhi on Tuesday of the Quad -- Australia, India, Japan and the United States.

He will also visit the palace-filled city of Jaipur on Monday to tour the Amber Fort.

Rubio is visiting four cities over four days in India as he seeks to revive ties with a country successive US administrations saw as a like-minded partner in a world dominated by China's rise.

Trump has shaken up that approach since returning to office, temporarily imposing high tariffs, warming to both China and India's historic adversary Pakistan, curbing visas used by Indian professionals and reposting insulting language about Indian immigrants.

Trump, in remarks Sunday by speakerphone to a celebration in New Delhi for the 250th anniversary of US independence, insisted he was on board with the relationship, telling the crowd, "we've never been closer to India, and India can count on me 100 percent".