Washington (AFP) - Pope Francis' popularity among Americans is rising, six months before his first papal visit to the United States, a public opinion poll released Thursday suggests.

Ninety percent of Catholic Americans surveyed by the Pew Research Center said they thought well of the 78-year-old pope -- and that includes 57 percent who held a "very favorable" view of him.

Among Americans of all faiths, 70 percent held a favorable view of the Argentinian-born pope -- the highest level since his papacy began in March 2013.

That compares to 57 percent when he became pope, 58 percent in September 2013 and 66 percent in February last year, Pew recalled.

Only 15 percent of Americans said they didn't like him, while another 15 percent claimed they could not rate him -- way down from 29 percent in March 2013.

"Among most US religious groups, Francis’ favorability rating has risen as more people have gained familiarity with the pope and become able to express an opinion about him," Pew said.

Many regard Pope Francis as a welcome change from his predecessor Benedict XVI, even as American bishops maintain a hard line against abortion and gay marriage.

Pope Francis is to visit the United States in late September to attend the World Meeting of Families in Philadelphia, Pennsylvania.

He is also expected to address the UN General Assembly in New York and become the first pope ever to speak to the US Congress in Washington.

Pew said it interviewed 1,504 American adults on landlines and cellphones on February 18-22 for its survey, which it posted at www.pewforum.org