The Russian and Ukrainian prime ministers have held talks over disputed territory on their coastal borders - but without solving the issue.
Russia says it is rebuilding a promontory that existed before
Russian Prime Minister Mikhail Kasyanov said that Moscow would halt work on a causeway across the Kerch Strait, between the Sea of Azov and the Black Sea, while Ukraine would withdraw border troops "immediately" from Tuzla Island.
But his Ukrainian counterpart, Viktor Yanukovych, said on his return to Kiev that no decision had been reached on withdrawing the guards.
Russian Foreign Minister Igor Ivanov will go to Ukraine at the end of next week for future talks on the issue.
An agreement on the status of the strait will be drawn up in two or three months.
Mr Kasyanov said that a joint working group would be set up to examine the need for the causeway which Russia is building from the mainland to Tuzla Island.
The construction work has now reached to within about 100 metres of Tuzla.
A BBC correspondent in the Crimea reports that official sources in the Kerch region of Ukraine say guards manning the Tuzla border post have been given no orders to leave.
Officials expressed concern that as soon as they left the island it would be occupied by either Russian border guards or Russian cossacks.
The correspondent reports that Russian builders were mending the causeway and building it higher on Friday after it was damaged by a storm, and covered with water.
The Ukrainian parliament passed a resolution on Thursday describing Russia's actions in building the causeway as an "unfriendly act".
At Friday's talks in Moscow, Russian Prime Minister Kasyanov described Ukraine's deployment of border troops as "an unjustified show of force".
"There are no borders there, so troops should not flex their
muscles there. We have agreed on that," he said.
President Kuchma visited the disputed area on Thursday
"The [Ukrainian] military must leave this strip of land immediately."
However, Ukrainian Prime Minister Yanukovych said Tuzla was "an inalienable part of Ukrainian territory".
Officials in the Russian region of Krasnodar say that Tuzla was once part of a promontory connecting it to Russian territory.
They say the work on the causeway is intended to protect the surrounding coastline.
Twelve years after the collapse of the former Soviet Union, the border between Russia and Ukraine has still not been demarcated.
At present, Russian shipping must pay transit fees to Ukraine for passage through the strait, which reportedly total several million dollars a year.