Ukraine's Foreign Ministry has expressed its deep concern to Moscow about developments in a growing row between the two countries over the construction of a Russian dam in the Black Sea's Kerch Strait.
Leonid Kuchma (r) has hardened his position against Russia
Spokesman Markiyan Lubkinsky said his government was unhappy with a Russian request for copies of the documents which support Ukraine's ownership of the tiny island of Tuzla in the strait.
He said it was unacceptable that Kiev should have to confirm the fact that the island was part of Ukrainian territory.
The Kerch Strait links the Black Sea with the Sea of Azov, separating Russia's Taman peninsula from the Crimean peninsula in Ukraine.
The row has now attracted the attention of Nato and the United States.
Washington has urged both sides to find a diplomatic solution to the problem, while Nato's secretary general is discussing the issue with the two countries' leaders during current visits to the former Soviet countries.
Russia says the dam, which is being built between Taman and Tuzla, is essential to protect its peninsula from erosion by the sea.
It also wants to share the area with Ukraine as internal waters - while Ukraine wants to divide both the waters and the seabed.
Russia began building the dam on 19 September. Ukraine fears Moscow will try to claim more territory ahead of border talks.
Ukrainian border guards have put themselves on alert, turned the Tuzla border post into a base, deployed anti-tank traps for the first time since World War II, and held air- and seaborne exercises near the island.
Ukraine's new Foreign Minister, Kostyantyn Hryshchenko, had to turn a familiarisation trip to Moscow on 6 October into emergency talks about the dam.
He was assured by his Russian counterpart Igor Ivanov that the dam would not violate the Ukrainian border, which runs 250 metres off the coast of Tuzla.
Ukrainian President Leonid Kuchma first considered the situation a "misunderstanding rather than politics".
But as the dam advanced, at a pace of over 100 metres a day, he hardened his position. On Friday he condemned it as an "unfriendly act".
The Ukrainian parliament expressed outrage at Russia's behaviour and, in an unusual cross-party show of unity, sent a delegation to Tuzla.
But correspondents say there is little public sympathy for an escalation of the crisis.
A poll published at the weekend showed most Ukrainians oppose the use of force. There is also general sympathy for Russia's position in Crimea, which has a large Russian population.
The Ukrainian and Russian foreign ministers are to discuss the Kerch Straits on 30 October in Kiev.
The only problem is that, if the current pace of construction continues, the dam will reach the Ukrainian border by 26 October.