Roger Waters and Alice Walker have penned open letters asking Alicia Keys to call off a forthcoming concert in Tel Aviv. Walker, the author of The Color Purple, invited Keys to join a cultural boycott of Israel, visiting "the children in Gaza" instead of supporting "a system that is cruel, unjust and unbelievably evil".

"Dear Alicia Keys," Walker wrote on the website for the US Campaign for the Academic & Cultural Boycott of Israel. "I have learned today that you are due to perform in Israel very soon. We have never met, though I believe we are mutually respectful of each other's path and work. It would grieve me to know you are putting yourself in danger (soul danger) by performing in an apartheid country that is being boycotted by many global conscious artists."

In his own letter, Waters admitted that Keys may not know who he is. "I used to be in a band called Pink Floyd and, believe it or not, I still work," he wrote. The English musician implored Keys to "join the rising tide of resistance" and refuse "to give legitimacy to the Israeli government policies of illegal, apartheid, occupation of the homelands of the indigenous people of Palestine."

Keys is due to appear at Tel Aviv's Nokia Arena on 4 July, as part of her ongoing Girl On Fire tour. It will be her first appearance in Israel. As the concert approaches, activists have begun ramping up their Facebook and Twitter campaign, asking the long-time HIV/Aids activist to consider dropping the gig in solidarity with the Palestinian rights movement.

"I have kept you in my awareness as someone of conscience and caring, especially about the children of the world," Walker went on. "A cultural boycott of Israel and Israeli institutions (not individuals) is the only option left to artists who cannot bear the unconscionable harm Israel inflicts every day on the people of Palestine, whose major 'crime' is that they exist in their own land, land that Israel wants to control as its own."

Elvis Costello, Santana, the Pixies and Gil Scott-Heron are among the other artists to have boycotted Israel in recent years, while acts including Madonna and Paul McCartney have dismissed calls to cancel shows. Earlier this month, physicist Stephen Hawking announced he was joining the movement, adding his name to a list of supporters that includes dozens of Nobel laureates.

Keys has yet to respond to activists' requests.