"It is premature to say that our concerns have been alleviated as talks have not yielded a satisfactory result," Lavrov told reporters in London, where he attended talks of the Middle East Quartet.
Lavrov said no progress has been made at talks on Russia's access to the proposed missile base and radar station in Poland and the Czech Republic. But he said the talks were continuing.
Moscow considers Washington's plans to deploy elements of its missile shield in Europe - which the U.S. says are needed to counter possible strikes from "rogue" regimes like Iran - a serious national security threat.
Lavrov said he was somewhat alarmed by U.S. officials' assessments of the agreements reached between the Russian and American leaders in the Black Sea resort of Sochi in early April as a solution to the missile dispute.
He said the Sochi declaration issued by Presidents Vladimir Putin and George W. Bush reflects Russia's opposition to the missile plans.
"The American side seems to have taken it into account and pledged to offer measures to boost trust and transparency in a bid to ease our concerns, but those measures have not been agreed on yet," the minister said.
Moscow has requested that Russian officers be given a permanent presence at the future missile sites in Europe.
Poland has been reluctant to allow Russian military personnel access to the planned site, however. The signing of a treaty on the deployment of a missile-defense radar between the Czech Republic and the U.S. has been postponed from May until June.