Chinese President Hu Jintao is returning home from Italy to deal with ethnic violence in China's Xinjiang province.
The Chinese state news agency Xinhua says the president cut short his visit and left for home early Wednesday. It says State Councilor Dai Bingguo will replace Mr. Hu at the summit of the Group of Eight and major developing countries later this week in the Italian city of L'Aquila.
The government in the western region of Xinjiang has declared a curfew following ethnic unrest that has paralyzed the main city of Urumqi. At least 156 people have been killed and about 1,000 others injured in rioting since Sunday.
China's top official in Urumqi, Communist party leader Li Zhi, said Tuesday authorities are blocking Internet access and mobile phone service in parts of the city in what they say is a measure to prevent further unrest.
Chinese foreign ministry spokesman Qin Gang said "foreign forces" are using those services to instigate violence.
Both officials blamed U.S.-based Uighur exile Rebiya Kadeer for organizing Sunday's rioting. Kadeer has denied any involvement.
The Foreign Correspondents Club of China complained that security forces in Xinjiang have detained and harassed foreign TV crews and other reporters.
In further unrest Tuesday, Muslim Uighurs and Han Chinese clashed with riot police in separate incidents.
Police first confronted about 200 mostly female Uighur protesters, who said members of their families had been arbitrarily arrested, after Sunday's riots.
Later in the day, riot police fired tear gas to disperse thousands of Han Chinese protesters who took to the streets armed with makeshift weapons, including clubs, shovels and knives.
The crowd vowed revenge on Uighurs and smashed shops and food stands operated by members of the ethnic group. Communist Party chief Li Zhi arrived on the scene, where he condemned Rebiya Kadeer in a speech to the crowd.
There were also reports that Uighur protests were held in the city of Kashgar, near Xinjiang's border with Pakistan.
Tensions between Han Chinese and Uighurs exploded last month, after a false rumor spread through a toy factory in Guangdong that Uighur workers raped two Chinese girls. A huge fight broke out, and two people were killed.
The official Xinhua news agency said Tuesday that police have arrested 15 people in connection with the racially-charged brawl, including two suspected of spreading rumors on the Internet.
State-run media said police have arrested 1,434 suspects in the clashes, which injured more than 1,000 people on Sunday.
As with last year's protests in neighboring Tibet, Chinese state media coverage has focused on ethnic Han victims.