SHANGHAI (Reuters) - Chinese President Xi Jinping reaffirmed his commitment to alleviating China's persistent rural poverty, only weeks after four children in a poor countryside area appeared to have killed themselves, sparking a national debate.

State media quoted Xi speaking on Thursday at a Communist Party conference about the 13th Five-Year Plan, which will set policy priorities for 2016-2020.

"The most arduous task for achieving a well-off society in an all-round way lies in the rural areas, especially the impoverished ones," he said.

Despite the rapid economic growth of the last two decades, poverty remains an issue in China, especially in rural areas where a lack of jobs drives able-bodied adults to work elsewhere, leaving children and the elderly behind.

The four children who died this month in the city of Bijie, in the poor southwestern province of Guizhou, were among those so-called "left behind" children, of which there are an estimated 60 million.

This was not the first such tragedy to strike the city. In 2012, five homeless children in Bijie died of carbon monoxide poisoning after lighting a fire while seeking shelter in a rubbish bin.

The seminar where Xi spoke was held in Guizhou.

According to the state-owned Xinhua news agency, Xi outlined four principles (dubbed the four "feasibles") that would guide poverty alleviation, including ensuring official responsibility, making sure policies were implemented with precision, pooling resources with society and strengthening grassroots organization.

China is expected to complete a draft of the 13th Five-Year Plan this fall and submit it to the National People's Congress, China's legislature, in March 2016.

(Reporting by Alexandra Harney; Editing by Nick Macfie)