US State Department's spokesperson Victoria Nuland made these remarks at a regular briefing Wednesday shortly after the US imposed additional sanctions on Syria by targeting its largest commercial bank and a largest mobile phone operator, Xinhua reported Thursday.
"This is very much the focus of the diplomacy that we're engaged with the Europeans, with Syria's neighbours, to encourage as we said yesterday as many countries as possible to take national action, to tighten the noose, to ensure that we do as much as possible to increase the pressure on Assad," she said.
Nuland said the US, Turkey and "an increasing chorus of countries" have made it clear to Assad "that the violence has got to stop, that the tanks have to go back to barracks, and that we have to start a real democratic transition."
In the latest round of sanctions, the US Department of Treasury targeted the state-owned Commercial Bank of Syria, its Lebanon-based subsidiary, Syrian Lebanese Commercial Bank and Syriatel, the largest mobile phone operator in the Arab nation.
US citizens are now prohibited from engaging in commercial or financial transactions with the Syrian entities, and their assets under US jurisdiction are frozen.
A number of Arab countries and Turkey have toughened their stance on Syria.
On Sunday, the six-nation Gulf Cooperation Council (GCC) in a statement, called for an immediate end to the violence and for a prompt implementation of reforms in Syria.