Venezuelan President Hugo Chávez will face a "complex and hard" process after undergoing his fourth cancer-related operation in Cuba, according to the country's vice president.

Vice President Nicolas Maduro made the announcement a day after Chávez's surgery, appearing on television with a sad expression, alongside other top allies of the president.

"It was a complex, difficult, delicate operation," Maduro said, adding that indicates "the post-operative process is also going to be a complex and hard process."

The vice president, whom Chávez named over the weekend as his chosen political heir, was flanked by National Assembly President Diosdado Cabello and Oil Minister Rafael Ramirez, who had accompanied the president in Havana during the surgery.

Maduro said Cabello and Ramirez had returned to Caracas about 3 a.m. and that they had talked about the situation until daybreak. Maduro's voice was hoarse and cracked at times.

Without giving details, he called for Venezuelans to calmly face potentially difficult days ahead.

"We're more united than ever," Maduro said, while Cabello and Ramirez stood solemnly. "We're united in loyalty to Chávez."

Maduro had said on Tuesday night that the operation concluded successfully after more than six hours and that Chávez next was to begin "special treatments," which he didn't specify. Chávez's children and grandchildren accompanied him in Havana during the surgery, the vice president said.

The morning after Chávez's operation, Venezuelan state television showed a Mass where the president's supporters prayed for him.

Chávez announced over the weekend that he needed to have surgery again after tests showed "some malignant cells" had reappeared in the same area of his pelvic region where tumors were previously removed.

Chávez said beforehand that the surgery would present risks. He said on Saturday for the first time that if illness cuts short his presidency, Maduro should take his place and be elected president to continue on with his socialist movement.

The 58-year-old president won re-election in October and is due to be sworn in for a new six-year term on Jan. 10. If Chávez were to die, the constitution says that new elections should be called and held within 30 days.

Chávez first announced he had been diagnosed with cancer in June 2011. He underwent a surgery for a pelvic abscess, and then had a baseball-sized tumor removed. In February, he underwent another surgery when a tumor reappeared in the same area.

He has also undergone months of chemotherapy and radiation treatments. Throughout his treatments in Cuba, Chávez has kept secret some details of his illness, including the exact location and type of the tumors.

Based on reporting by The Associated Press.

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