TUCSON, Ariz. — U.S. Rep. Raúl Grijalva announced Tuesday that he has been diagnosed with cancer, but he said he is continuing to work while undergoing treatment.

''A few weeks ago, I sought medical treatment for a persistent cough which was initially diagnosed as pneumonia. After further testing and imaging, my physician discovered that I have cancer,'' the 76-year-old Democrat, who is the dean of Arizona's congressional delegation, said in a statement.

''This diagnosis has been difficult to process, but I am confident in the vigorous course of treatment that my medical team has developed, and I've begun my journey to fight this cancer," Grijalva added.

It is unclear what type of cancer Grijalva has. The congressman's office said no other information was being released at this time.

''I am working hard to get healthy and return to business as usual as soon as I am able,'' said Grijalva, who was first elected to the U.S. House in 2002 and is seeking a 12th term in this year's election.

Ruben Reyes, who works for Grijalva as his Southern Arizona district director, said he didn't think the cancer treatment will affect the congressman's ability to do his job.

The district Grijalva represents spans most of the Arizona-Mexico border and includes sections of Cochise, Maricopa, Pinal, Santa Cruz and Yuma counties.

''My congressional office remains open and the many services we provide for our constituents continue uninterrupted. I am in regular communication with my staff,'' Grijalva said in his statement. ''It is a privilege to serve as a Representative for the people of Arizona and take this responsibility very seriously.''