"These initiatives are formulated in a manner that allows the Americans to back down on their promises at any time," Lt. Gen. Yevgeny Buzhinsky, head of Russia's Defense Ministry international cooperation department, told the Rossiiskaya Gazeta daily.
Moscow has strongly opposed the possible deployment by the U.S. of 10 interceptor missiles in Poland and a radar in the Czech Republic as a threat to its security and nuclear deterrence. Washington says the defenses are needed to deter possible strikes from "rogue states."
During their visit to Moscow in late March, U.S. Defense Secretary Robert Gates and Secretary of State Condoleezza Rice offered to let Russia monitor the proposed U.S. missile and radar bases in Central Europe.
Washington has also said it will not activate the system until there is a "clear and present" threat from Iran or other potential adversaries.
But the Russian general said: "The [U.S.] proposals are accompanied by some conditions that are totally unacceptable to us."
"For instance, the proposed document does not mention Russia's right to take adequate measures if Washington suddenly decides to add new elements to its missile defenses in Europe, or increase the number of deployed interceptor missiles..," Buzhinsky said.
"It would be naive to hope that we would not take retaliatory measures in response to such actions," he added.
He was not specific about the nature of these retaliatory measures, but former Russian president Vladimir Putin earlier warned that Russia could point nuclear missiles at countries that accept U.S. missile defense components.
Washington also suggested that Russia negotiate directly with Poland and the Czech Republic on giving Russian officers permanent access to the planned facilities, but Buzhinsky said the talks had stalled, because both Polish and Czech officials categorically refused to allow the permanent presence of Russian military personnel on their territory.
"Such conditions transform an apparently reasonable initiative into useless rhetoric," the general said.
"Besides, the proposed document says the agreements between Moscow and Washington [on the European missile shield] could be unilaterally cancelled as soon as the U.S. concludes that a missile threat has become imminent," Buzhinsky said.
"This means that the Americans can activate their missile shield at any time, without giving sufficient prior warning," he added.
U.S. Secretary of State Condoleezza Rice is expected to sign a missile shield agreement with the Czech Republic during her European tour on July 8-10.
The Czech government has already agreed to the U.S. plans, pending parliamentary approval.
However, Polish-American talks on Washington's plans to place 10 interceptor missiles in Poland as part of its missile defense shield have stalled. Poland's prime minister said last Friday his country was not satisfied with the terms offered by the U.S., but was ready for further dialogue.