The president of newly independent South Sudan, in Beijing lobbying for economic and diplomatic support, told China's president on Tuesday that attacks by rival Sudan amount to a declaration of war on his country.

There has yet to be a formal declaration of war by either of the Sudans, and Salva Kiir's remark, made during talks with President Hu Jintao, signals a ratcheting up of rhetoric between the rival nations which have been teetering on the brink of war.

Kiir arrived in China late Monday for a five-day visit. He told Hu the visit comes at a "a very critical moment for the Republic of South Sudan because our neighbor in Khartoum has declared war on the Republic of South Sudan."

South Sudan broke away from its neighbor and became independent last year. The two countries have been unable to resolve disputes over sharing oil revenue and determining a border. Talks broke down this month.

On Monday, Sudanese warplanes bombed a market and an oil field in South Sudan, killing at least two people after Sudanese ground forces had reportedly crossed into South Sudan with tanks and artillery.

Sudanese President Omar al-Bashir has vowed to press ahead with his military campaign until all southern troops or affiliated forces are chased out of the north.

Kiir told Hu that he came to China because of the "great relationship" South Sudan has with China, calling it one of his country's "economic and strategic partners."