WASHINGTON - President Obama moved to tighten sanctions on Syria and Iran on Monday by taking aim at those who provide their authoritarian governments with technology to track down dissidents for abuse, torture or death. The measures underscored the role that computers, social media and cellphones have played in the recent political upheavals in the Middle East, not just in organizing resistance to entrenched leaders, but also in helping security services crack down on protesters. The president's action is meant to put on notice individuals and companies that provide the technology that enables human rights abuses. The announcement came as Mr. Obama continues to search for a more effective response to the killings in Syria, where more than 9,000 people have died over the past year as the government of President Bashar al-Assad has tried to suppress a popular uprising. It's one more step that we can take toward the day that we know will come, the end of the Assad regime that has brutalized the Syrian people. The new measures reflect the rapidly evolving nature of the political struggles in the Middle East. "I'm sure countries like Sudan, Syria and others are watching closely what's happening on Facebook," said Michael Abramowitz, director of the Holocaust museum's Committee on Conscience. They don't need to send plainclothes men to follow activists anymore. They can follow them online. Mr. Obama made the announcement at the emotionally symbolic museum after touring the exhibits alongside Elie Wiesel, the Holocaust survivor and Nobel Peace Prize laureate. Mr. Wiesel, invoking the Holocaust, used the occasion to implore Mr. Obama to stand against Mr. Assad and President Mahmoud Ahmadinejad of Iran. Have we learned anything from it? Mr. Wiesel said. If so, how is that Assad is still in power? How is it that the No. 1 Holocaust denier Ahmadinejad is still a president? Mr. Obama, who has been criticized over his Israel policy, presented himself as a staunch defender of the Jewish state and vowed to counter the threat to it posed by Iran. The executive orders, which Mr. Obama signed Sunday and were first reported by The Washington Post, authorize financial and travel restrictions against those who aid the Syrian and Iranian governments in using technology to hunt down their own citizens. Among those first targeted were Datak Telecom, the Iranian Internet service provider, and Syriatel, the Syrian communications company. The White House said that the restrictions were primarily aimed at entities based inside the two countries, but that American technology companies had been consulted and understood that compliance would now be part of their standard due diligence in international contracts. Mark Dubowitz, executive director of the Foundation for Defense of Democracies, a nonprofit research organization, said the sanctions would be most useful if they took aim at a company like ZTE, the Chinese telecommunications manufacturer, which has sold systems to Iran used for surveillance of dissidents. "For this executive order to have any impact, it has to go after a company like ZTE," he said. If it doesn't, it has far less significance, because the reality is we have a trade embargo against Iran. There's a thicket of very strict sanctions law already in place. The real value in U.S. sanctions is when they're secondary sanctions. The steps announced by Mr. Obama were the latest attempt to develop a broader strategy to respond to genocides and other mass killings after the failure of his two predecessors to prevent widespread slaughter in Rwanda and Darfur, Sudan. Among other things, the president said that the nation's intelligence agencies would conduct a full-scale study of the risks of future mass killings, and he promised more aggressive diplomatic, financial and humanitarian actions. Mr. Obama signed a presidential directive in August declaring that "preventing mass atrocities and genocide is a core national security interest and a core moral responsibility of the United States of America." But the 100-day review stretched on for 263 days, until the president announced its results on Monday, when the atrocities board was scheduled to convene for the first time, despite months of killings in Syria. Mr. Obama, who was making his second visit to the Holocaust museum, placed a candle in front of the Buchenwald section of its remembrance wall in honor of his great-uncle who served in an American military unit that liberated a subcamp of Buchenwald.