Not long ago, things were looking up when it came to U.S.-Russian relations and the possibility for some level of cooperation on missile defense in Europe.

Now, they’re looking down. Again.

On Thursday, a day after the Obama administration and the Spanish government announced they would base Aegis Cruisers on Spain’s coast, the Russian government issued a statement condemning the agreement and threatening to scuttle any cooperation with the United States.

The agreement, it said, was made “without collective discussion” and raised concerns about a “significant build-up of U.S. missile potential in the European zone.”

The missile shield in Europe, the Obama administration says, is intended to protect against any ballistic missile strikes from Iran or other hostile countries. But Russia has long seen plans for the shield as a stalking horse to neutralize its own defenses.

Earlier this year, there were signs of rapprochement, as the Russians and Americans held a series of exploratory talks about sharing data from sensors that could detect the launch of missiles. It was a new day, and even if significant differences remained, there was a sense that there was no other option but to negotiate.

In Moscow, President Dmitry Medvedev said the alternative to collaborating with the United States and NATO on missile defense was “a new arms race,” which Russia could not afford.

But on Thursday, following the Spain deal — and an agreement last month between the United States and Turkey — the signs from Moscow were less positive.

“Not only do we see no readiness on the part of the U.S. administration to address Russia’s concerns about the key issue of guaranteeing that the future system will not be aimed at Russia’s strategic nuclear arsenal, we also note the tendency to increasingly expand treat the deployment areas of the U.S. anti-missile systems,” the Foreign Ministry said.

“If this continues,” it added, “then the chance ... to turn anti-missile defense from an area of confrontation to an area of cooperation may be lost.”

Development of a European missile shield accelerated under the administration of George W. Bush, whose plans included interceptors in Poland and a radar installation in the Czech Republic.

Two years ago, Obama announced that he was overhauling that plan, and would rely more heavily on anti-ballistic missile radars and interceptors based on Navy ships in the Mediterranean Sea.

If all goes according to plan, the shield will be completed, in phases, by 2020.