Lagos, Nigeria (CNN) -- Ailing President Umaru Musa Yar'Adua has returned home to Nigeria, though it was not immediately clear whether he was well enough to resume duties.





Abdullah Aminchi, Nigeria's ambassador to Saudi Arabia -- where Yar'Adua has been receiving medical treatment since November -- said the president's health had improved considerably and that he went back to Nigeria on Tuesday.





He was treated for inflammation of tissue around the heart, a condition that was diagnosed last fall after he complained of chest pain. He was taken to King Faisal Specialist Hospital and Research Centre in Jeddah, Saudi Arabia, where he had undergone his last checkup in August, his doctor said





His absence had created a power vacuum in Africa's most populous nation, observers said. It also sparked demonstrations in the nation's capital, Abuja, where protesters demanded a constitutional order on his absence and evidence about his true state of health.





Explainer: Will Nigeria's leader return to power?





As a fix, Nigerian lawmakers voted earlier this month to install the country's Vice President Goodluck Jonathan as head of state.





A statement from the U.S. assistant secretary of state for the Bureau of African Affairs Wednesday welcomed the news of Yar'Adua's return, but said he hoped that it was not "an effort by his senior advisors to upset Nigeria's stability and create renewed uncertainty in the democratic process."





"Nigeria is an extraordinarily important country to its friends and partners, and all those in positions of responsibility should put the health of the president and the best interests of the country and people of Nigeria above personal ambition or gain," said the statement from Assistant Secretary of State Johnnie Carson.





"As a nation of 150 million people, Nigeria's democracy and its continued adherence to constitutional rule should be the highest priority," the statement added.
who was treated how long was he absent Who is unclear to resume duties? What did his absence create? What has he been treated for?
Umaru Musa Yar'Adua since November President Umaru Musa Yar'Adua a power vacuum inflammation of tissue around the heart,
question: who was treated, answer: Umaru Musa Yar'Adua | question: how long was he absent, answer: since November | question: Who is unclear to resume duties?, answer: President Umaru Musa Yar'Adua | question: What did his absence create?, answer: a power vacuum | question: What has he been treated for?, answer: inflammation of tissue around the heart,