A Chinese government official in the restive region of Xinjiang denied there had been a new blast on Monday, however.
A spokesman for Uighur exiles said in Almaty, capital of neighbouring Kazakhstan, said that the acts were in reprisal for deaths and arrests during a Chinese clampdown on the separatist movement over the past month.
"We intend to continue our struggle," Mukhiddin Mukhlisi added, saying three exile groups had joined forces after police and army killed 127 Uighurs and arrested hundreds more.
An official in Urumqi, capital of Xinjiang province, said at the weekend that seven people had died and 60 were hurt in three time-bomb explosions on buses in the city on 24 February, coinciding with funeral rites for China's leader, Deng Xiaoping.
Mr Mukhlisi said he did not know how many victims there were in the latest attack on Monday on a bus travelling to Urumqi from Yining, near the Kazakh border. The blast occurred 120km (75 miles) east of Yining, he said.
"The explosion in the bus near the town of Kuldji [Yining] ... was our act of revenge for the crimes of the Chinese authorities," Mr Mukhlisi said.
However, a government official in Yining said by telephone: "It's peaceful here. There was no new bomb attack."
A spokesman for Uighur exiles in Russia, Sargari Tarym, said last week in Moscow: "We think Deng's death will bring a power struggle within the Chinese elite. If that happens, the independence movement in Turkestan will intensify."
Mr Mukhlisi said Peking had launched a "hundred days anti-separatist campaign" against Uighur nationalists who want to establish an independent "East Turkestan" homeland.