With tension rising in Tibet following a series of anti-China protests, the BBC spoke to an eyewitness who saw police on Wednesday beating monks at one of three monasteries which have been sealed. He wishes to be identified only as John.
Monks clashed with security forces at Sera monastery on Wednesday
We knew something was happening because there were more road checks as we got into Lhasa.
Cars were being stopped and police were writing the licence plates down. We tried to stop at a shrine outside Lhasa but were told to keep moving.
Then we heard around Wednesday lunchtime that Drepung monastery was closed. We didn't know why.
That afternoon we went to Sera monastery to see the debating. It's famous - the monks debate points of philosophy and people come to see it.
Just when it was about to start, around three o'clock, we started to hear rounds of applause coming out of a courtyard in the heart of the temple.
They were grabbing monks, kicking and beating them
We thought the debate was starting but then suddenly the clapping reached a crescendo - kind of a hooting.
Then the gate of the debating compound opened and this stream of maroon humanity poured out, several hundred monks. It was impossible to count but I think there were at least 300.
We thought it was part of the tradition but when you looked at the expression on their faces, it was a very serious business. They were pumping their hands in the air as they ran out of the temple.
The minute that happened we saw the police - two or three who were inside the compound - suddenly speaking into their radios.
They started going after the monks, and plain-clothes police - I don't know this for sure but that's what I think they were - started to emerged from nowhere.
There were four or five in uniform but another 10 or 15 in regular clothing. They were grabbing monks, kicking and beating them.
If we had gone to Sera monastery an hour earlier or an hour later, no-one would have known what these monks had done
One monk was kicked in the stomach right in front of us and then beaten on the ground.
The monks were not attacking the soldiers, there was no melee. They were heading out in a stream, it was a very clear path, and the police were attacking them at the sides. It was gratuitous violence.
The Tibetan lay-people started rushing to get out of the temple. Tibetan grandmothers were grabbing young kids and getting them out.
We were left behind when the monks left the temple. About 20 minutes later we felt as if we could leave.
Outside the monastery the road curved to the left and to the right. We were directed left - but when we looked to the right there was a line of riot police with batons and helmets blocking off the street.
The monks were sitting in neat rows on the ground, surrounded by a phalanx of police. It was a very clear show of force - there were maybe as many as 300 riot police and regular police there.
It could have been civil disobedience, but it looked like the monks had been put there. They weren't moving.
As we turned left, we saw troop carriers with camouflaged army regulars arriving - those green trucks with soldiers in the back on benches. We saw guns, large guns that looked like automatic weapons.
There were two or three of those trucks as well as others - several units of public order personnel swarming the situation.
As we left, all the roads around the monastery were blocked by police. There was no access.
At the time, all the phones were dead - we were trying to call the hotel but none of the cell phones were working. But within an hour the phone service was back on.
It seemed as if within half an hour the thing had been totally brought under control.
Back in Lhasa, it was eerily normal. There were police around but not really a muscular presence. It seemed to have been a massive localised show of force.
We realised that if we had gone to Sera monastery an hour earlier or an hour later, no-one would have known what these monks had done.