The US president has announced a new crackdown on Iran and Syria to pressure entities that use information technology to commit human-rights abuses.

Obama signed a new executive order permitting the penalties on Monday, the treasury department slapped sanctions on six Iranian and Syrian companies or government branches along with the head of Syria's intelligence directorate.

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The sanctions freeze any assets they may have in US jurisdictions and ban US citizens from doing business with them.

Six of the seven - Iran's Revolutionary Guard Corps, national police, and intelligence ministry as well as the Syrian intelligence chief and his agency and the state-controlled cell phone company - were already subject to US sanctions.

The new addition is Iran's Datak Telecom internet provider.

In his first appearance as president at the US Holocaust Memorial Museum, Obama broadly defended his government's steps to protect innocent people, saying: "We have saved countless lives".

His words come as the US faces pressure to help rally an international solution in Syria, where President Bashar al-Assad is accused of running a lethal crackdown on his people.

"National sovereignty is never a licence to slaughter your people," Obama said.

Role of technology

While rebellions in countries like Libya and Egypt have been driven by cellphones and social media, other regimes have used technology to track dissidents or block internet access.

For example, Iran has provided Assad's regime with technology to jam cell phones and block or monitor the social networking sites rebels might use to organise demonstrations.

Obama has also asked the US intelligence community to include assessments of the likelihood of mass killings in its National Intelligence Estimates.

The White House announced a set of "challenge" grants for companies that help create new technologies to help warn citizens in countries where mass killings may occur.

Before delivering remarks, Obama spent about 30 minutes touring the war museum with the Nobel laureate and Holocaust survivor, Elie Wiesel.

To Wiesel, Obama said: "You show us the way. If you cannot give up, if you can believe, then we can believe".

Obama also announced he would be giving a posthumous Presidential Medal of Freedom to Jan Karski, a wartime emissary of the Polish government-in-exile who was among the first people to provide accounts of the Holocaust to the world.