However, Gang declined to comment on their fate.
 
On Monday, 300 monks set out from Drepung monastery on the outskirts of Lhasa to the city centre, according to a report by Radio Free Asia, a US-funded broadcaster.
 
The report said between 50 and 60 marchers were arrested when police and paramilitary forces prevented the protest from growing by blocking roads and monasteries around Lhasa.
 
The march coincided with the 49th anniversary of a failed uprising against Chinese rule in Tibet.
 
Marchers defy ban
 
Separately on Tuesday about 100 Tibetan refugees in India vowed to defy a police ban and march to Tibet.
 
On Monday they set off from the town of Dharamsala, home to the Dalai Lama, Tibet's exiled spiritual leader.
 
But on Monday evening Indian police said the marchers were banned from leaving the Kangra district of Himachal Pradesh state, until further notice.
 
On Tuesday they continued to march as planned and said they expected to reach the borders of the district by Thursday evening.
 
Tsewang Rigzin, president of the Tibetan Youth Congress, said: "Tibetan refugees have the right to return to Tibet.
 
"This is the first major obstacle we are facing, but we remain committed to marching."
 
Atul Fulzele, a Kangra police superintendent, told Reuters news agency he had received orders from the central government to restrain the marchers.
 
As the Olympics approach, Tibetans are trying to reinvigorate their freedom movement and protest against what they see as China's illegal occupation of their homeland.
 
The protests marked the anniversary of a 1959 uprising in Tibet against Chinese rule, which was crushed by the People's Liberation Army.
 
The Dalai Lama last week rejected a Chinese accusation that he was trying to sabotage the Olympics, saying he supports Beijing's right to host the games.