The 56-nation Organization for Security and Cooperation in Europe started its annual council of ministers meeting in the Spanish capital, following its declaration that it would not monitor Russia's parliamentary elections on December 2.
"The OSCE has united us in the struggle to construct a Europe at peace with itself," Jose Luis Rodriguez Zapatero.
He also stressed the need for a new consensus on the Conventional Forces in Europe (CFE) Treaty, which he called "the cornerstone of peace."
Russia said earlier it would freeze its participation in the treaty in protest against U.S. intentions to deploy missile defense elements in Central Europe.
He also said that he was optimistic that progress could be made in the dispute with Russia over the treaty, but said a major agreement was unlikely in Madrid.
After the OSCE's Office for Democratic Institutions and Human Rights (ODIHR) announced that it would not be attending Russia's parliamentary elections, President Vladimir Putin accused the United States of putting pressure the organization.
Washington had earlier accused Russia of trying to undermine the OSCE's election work, with a senior U.S. government official claiming that Russia was seeking to weaken the OSCE and its election monitoring mission.
He said Russia was working to "cripple" the ODIHR.
Russia said earlier on Thursday it would invite the ODIHR, which refused to attend December's parliamentary polls, to observe next year's presidential elections.
Speaking to reporters in Madrid, Sergei Lavrov said he was uncertain as to how the ODIHR would respond to Russia's invitation to the March 2, 2008 elections.
"I can't say what the ODIHR's reaction will be, because it is really unpredictable," Lavrov said.
He said Russia had done everything it was obliged to and observed its commitments to invite international observers to the elections, adding that the ODIHR chief in a recent interview had said the decision not to send monitors to the parliamentary elections was down to visa problems.
He described the U.S. position on the issue as "unconstructive."
Although the OSCE is recognized by Western countries as the main authority on election monitoring, whose approval is a key requisite to declaring elections free and fair, Russia has in the past accused the organization of bias toward pro-Western opposition parties.
The OSCE played a key role in unveiling alleged ballot rigging in the 2004 Ukrainian presidential elections, leading to an election re-run in which a pro-Western candidate, Viktor Yushchenko, defeated his pro-Kremlin rival Viktor Yanukovych.