Uzbekistan President Islam Karimov and Chinese President Xi Jinping on Monday signed agreements worth $15 billion in key sectors, including the exploitation of oil, gas, and uranium fields in the Central Asian state.

In the latest stop on Xi's tour of Central Asia, President Karimov praised his energy-rich country's growing ties with China which he described as the locomotive of the world economy.

"For all the years of our independent development, China has never linked the provision and expansion of multifaceted bilateral cooperation with any political or other conditions," Karimov told reporters.

This appeared a veiled reference to Tashkent's sometimes awkward relations with the West over human rights concerns.

Xi is on a closely-watched four nation tour of Central Asia that has already seen him sign major energy deals in Turkmenistan and Kazakhstan. He is later due to travel to Kyrgyzstan.

China over the last years has been ramping up its influence in a region that was once Moscow's playground, seeking new sources of energy for its fast-growing economy.

The two sides also inked a document to make changes to an Uzbekistan-China gas pipeline agreement signed a few years ago.

The changes were due to the planned construction of a fourth branch of the Turkmenistan-China gas pipeline that runs through Uzbekistan and Kazakhstan.

Since 2002 China has invested more than $6 billion in the Uzbek economy, and the volume of bilateral trade reached $3.4 billion last year, according to the Uzbek president.

"One of our priorities is to increase the trade turnover between our countries to $5 billion by 2017," Xi said.

The Chinese president will also visit the ancient Silk Road town of Samarkand, where a Confucius Institute -- China's equivalent to British Councils or Goethe Institutes -- is expected to open.

"I have long dreamt of visiting ancient Samarkand... and it is a great honour for me that president Karimov is accompanying me to his hometown," Xi said.