By Helen Fawkes
The president of Ukraine, Leonid Kuchma, has sent three top security chiefs to Crimea to investigate ethnic conflict in the region.
The ethnic tension comes on the eve of a sensitive anniversary
Three people have been stabbed in Crimea since Tuesday in fighting between Crimean Tartars and Ukrainians.
The incidents sparked a protest involving hundreds of Crimean Tatars.
Ukraine's prosecutor-general, interior minister and the security service's deputy head are due to start their work in the Crimean capital on Thursday.
The trouble flared on Tuesday when a young Crimean Tartar was attacked with a knife by a gang of men in the Crimean capital of Simferopol.
This led to violence between groups of Crimean Tartars and Ukrainians.
Two men were stabbed and a number of people were arrested.
On Wednesday, more than 600 Crimean Tartars protested outside the city's police station.
There has been conflict between Ukrainians and Crimean Tartars in the past.
But it is feared there will be an increase in ethnic tension as the 60th anniversary of the forced deportation of Tartars from the Crimea is in May.
Tartar leaders - who are calling for greater rights, especially over land distribution - are expected to organise a series of protests to mark the anniversary.
Around 200,000 Crimean Tartars were exiled to central Asia; an estimated 40% died in the first few years.
It was only during the break-up of the Soviet Union in the 1990s that they were allowed to return to the Crimea.