Police fired tear gas and bullets to disperse the protesters
A senior separatist and four others have been killed after police in Indian-administered Kashmir fired shots to disperse stone-throwing Muslims.
Sheikh Abdul Aziz was among thousands of protesters who marched towards the Line of Control (LoC) dividing the region. Dozens of others were hurt.
They were supporting a move by fruit growers in the mainly Muslim Kashmir valley to take produce across the LoC.
Tensions are rising and threaten peace hopes after years of relative calm.
The BBC's Chris Morris in Delhi says the Indian government was slow to realise how volatile the situation had become - and opposition parties were quick to try to use the situation to their own advantage.
He says the result is that Kashmir has reached a very dangerous point - more divided along communal lines than it has been for years.
Thousands of fruit growers and other protesters began their march on Monday from Sopore, 50km (30 miles) north of Srinagar, the summer capital of the state of Jammu and Kashmir.
Sheikh Abdul Aziz was a prominent leader of the All Party Hurriyat Conference, which opposes Indian rule.
He and four others were killed when local police opened fire on the demonstrators, reports said. An indefinite curfew has now been imposed in Srinagar.
If the blockade continues it will be a disaster for us
Mohammad Yousuf, Kashmir Fruit Growers' Association
Police say several of their personnel were injured by stones thrown by those at the protest.
The demonstrators were attempting to march to the de facto border with Pakistani-controlled Kashmir to protest at a blockade by Hindus in the Jammu region of a key highway that links the Kashmir Valley with the rest of India.
Hindus have protested for weeks since plans were scrapped to give land to a Hindu trust to build facilities for pilgrims near an important shrine in the region.
With the highway blocked for days, the Muslim fruit growers have complained that their produce is rotting.
Dozens of protesters were injured, some after being beaten by police
"We have suffered a loss of at least 20m rupees [about $475,000] since this agitation began," Mohammad Yousuf, president of the Kashmir Fruit Growers' Association, told the Reuters news agency.
"And if the blockade continues it will be a disaster for us."
In the Qamarwari area of Srinagar, police also fired rubber bullets to break up a demonstration of thousands of people.
Senior separatist leaders have been placed under house arrest.
The Indian Home Minister, Shivraj Patil, has appealed to the fruit growers to call off their protests.
He has offered to buy all their fruit and also to pay compensation to those whose fruit has perished.
The row started when the state government said it would grant 99 acres (40 hectares) of forest land to the Amarnath Shrine Board.
Muslims launched violent protests, saying the allocation of land was aimed at altering the demographic balance in the area.
The state government said the shrine board needed the land to erect huts and toilets for visiting pilgrims.
But following days of protests, the government rescinded the order, prompting Hindu groups to mount violent protests of their own.
About 20 people - Muslims and Hindus - have been killed and hundreds wounded in clashes with police since the unrest began.
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