The US government said on Tuesday that it is not considering arming the opposition in Syria, as violence continues in an 11-month turmoil facing the Arab nation.

"We're not considering that step right now," White House spokesman Jay Carney told reporters at a regular news briefing.

"We're exploring the possibility of providing humanitarian aid to Syrians, and we're working with our partners, again, to ratchet up the pressure, ratchet up the isolation on Assad and his regime," he said.

US Senator John McCain on Tuesday called for arming the Syrian opposition, saying "We should start considering all options, including arming the opposition. The bloodletting has got to stop. "

The call came as the UN Security Council failed to agree over the weekend on a resolution backing an Arab League initiative that seeks the ouster of Syrian President Bashar al-Assad for a political transition.

"We don't think more arms into Syria is the answer," State Department spokeswoman Victoria Nuland said.

"We think the answer is to get to a national democratic dialogue, for the violence to stop, for the regime's tanks to come out of the cities, and then for monitors to be able to go back," she said at a regular news briefing.

She rejected a comparison with Libya, where the opposition toppled long-time leader Muammar Gaddafi under the cover of NATO air strikes, saying "Libya was a completely different situation."