"The demonstration, which started in front of the Finnish parliament and ended two hours later at the Finnish foreign ministry, was organized by the Kurdish Organization in Finland and was peaceful," Helsinki police chief inspector Heikki Kallio told AFP.

Ocalan, 58, led a bloody separatist rebellion in southeast Turkey from 1984 until his capture in 1999.

His lawyers claim that laboratory tests on his hair samples have indicated the presence of what they described as toxic metals, including levels of chromium seven times higher than normal and high levels of strontium.

Finnish media reported that Thursday's demonstrators had sent a letter addressed to the Finnish foreign minister in which they expressed their concerns about Ocalan's health.

But the foreign ministry said it had no knowledge of such a letter.

"Maybe it is in the mail," a spokesman said.

Ocalan's Kurdistan Workers' Party (PKK) is listed as a terrorist group by Ankara and much of the international community, but to many among Turkey's sizeable Kurdish minority its militants are freedom fighters.

The PKK campaign for Kurdish self-rule in the southeast has resulted in more than 37,000 deaths.