Clashes between protesters and troops erupted in the Uzbek town of Andijan in mid-May and witnesses said more than 500 people had been killed when troops moved to end a protest against what many saw as an unfair trial of a group of local businessmen. Some organisations put the death toll as high as 1000.
The Uzbek government puts the death toll at 169.
President Islam Karimov says his government deployed force as an emergency response to an attempt by dozens of armed Islamic extremists, supported by local residents, to overthrow the government.
"As to what happened in Uzbekistan recently, it is basically a domestic affair; but we firmly support the crackdown on the three forces of separatism, terrorism and extremism by the Uzbekistan government," China's Foreign Ministry spokesman Kong Quan told a news conference on Tuesday.
China has been concerned about separatism among its Turkic-speaking ethnic Uighur minority in the far-western Xinjiang region and is wary of unrest on its borders.
China is concerned about minority
separatism on its own borders
It had temporarily closed a crossing between Xinjiang and Kyrgyzstan in March when opposition forces seized power after days of violent protests.
"We support the efforts by the Uzbekistan government to stabilise the domestic situation and to engage in national development," Kong said.
Source of oil
He added that fighting separatism, terrorism and extremism was a key goal of the Shanghai Cooperation Organisation. China has played a major role in this Central Asia security forum, in part because it sees the region as a strategically important source of oil.
Karimov is due to meet Chinese President Hu Jintao and Premier Wen Jiabao on his visit, which runs until Friday.
Karimov, who has ruled Uzbekistan since independence from the Soviet Union in 1991, has been criticised for the slow pace of reform in the country. He has defended his rule by saying Islamic fundamentalists want to overthrow his government.
He is also a key US ally in its fight against Taliban and al-Qaida remnants in neighbouring Afghanistan.
Meanwhile, Nato has voiced deep concern at the clampdown in Uzbekistan, warning that the ex-Soviet state's links with the alliance were dependent on its commitment to basic freedoms.
"Nato is deeply disturbed by the recent violence in Uzbekistan. We condemn the reported use of excessive and disproportionate force by the Uzbek security forces," said the 26-nation bloc in a statement on Tuesday.
Uzbekistan has been part of Nato's Partnership for Peace programme since 1991, shortly after the collapse of the Soviet Union, offering it closer military and political ties with the West's former Cold War-era military bloc.
Uzbekistan's special forces
soldiers on a truck in Andijan
"The alliance expects all its partners to fulfil their commitments to basic freedoms, human rights and other fundamental values," it said, noting that Tashkent has undertaken to adhere to those values in becoming a Nato partner.
"We will keep our relationship with Uzbekistan under close review, and call for transparency, co-operation with international organisations and domestic reform to strengthen democracy and the protection of human rights," it said.
Nato also reiterated its backing for a UN call for an independent international inquiry into these events and urged the Uzbek authorities to allow such an investigation. Karimov has rejected calls for an inquiry.