CARACAS, Venezuela — President Hugo Chavez made an unannounced return to Venezuela on Saturday night after spending a week in Cuba undergoing chemotherapy, saying that he expects a series of additional cancer treatments will take time.

State television broadcast footage of Chavez being greeted at the airport by Vice President Elias Jaua and other ministers. Addressing the nation, Chavez said the chemotherapy in the past week went well but that risks remain and he expects his treatments to continue for an extended period. He did not say how long.

"It's important that the Venezuelan people don't believe that everything is done," Chavez said. "We're in a complete process of fighting very hard, and it takes its time. We're winning it and we'll win it, but it takes its time and its rhythms."

The 56-year-old president underwent surgery in Cuba on June 20 to remove a cancerous tumor, which he said was the size of a baseball. He hasn't said what type of cancer he has been diagnosed with or specified where exactly it was located, saying only that it was in his pelvic region. He says chemotherapy is necessary to ensure cancer cells don't reappear.

Chavez said that a day after he arrived in Cuba on July 16, he underwent "intense studies that they call medical imaging." He said 126 images showed that "no presence of malignant cells was detected in any part of my body."

"In any case the risk exists," Chavez added. "For that reason the chemotherapy, which was given to me the whole week in various sessions."

Chavez said Friday that he had successfully completed a "first cycle" of chemotherapy and will next begin the second of various additional stages. He did not when the next series of chemotherapy treatments would begin.

"I address the country from my heart to express my immense happiness and gladness to be in Venezuela after one week," Chavez said in his brief televised speech late Saturday night. "Throughout this week, I haven't lost an instant in my attention to Venezuela — what happens, the problems, the solutions."

The leftist president, who has been in power since 1999, has said he intends to run for re-election in late 2012 despite his illness.

"After this week of intense work in Cuba with a quality Venezuelan and Cuban medical team, I should tell you... that I've come back better than I left," he said.

Chavez also thanked his Cabinet ministers for coming quickly to the airport for his arrival, which was not previously announced.