Cambodia's former king, Norodom Sihanouk, will delay his return from China to undergo further treatment of a cancerous tumor, a gastric lymphoma.

The 82-year-old former monarch has been in Beijing for medical treatment since January, but until now he had been expected to return to Phnom Penh on May 8.

In a statement posted on his Web site Sunday, King Sihanouk said Chinese doctors advised to remain in Beijing for further treament, because they consider the tumor "very serious". His cancer was believed to have been in remission since chemotherapy treatment in the early 1990s.

King Sihanouk yielded his throne last October to his son, King Norodom Sihamoni. He had been planning to return home this week to head a new effort to resolve border disputes with Cambodia's neighbors Laos, Thailand and Vietnam.

Some information for this report provided by AFP and AP.