"It's too soon to call an outcome." He said Yemeni President Ali Abdullah Saleh had been a valuable partner for Washington's fight against Al-Qaeda militants but acknowledged rising popular discontent in the country.

"We have had a good working relationship with President Saleh. He's been an important ally in the counter-terrorism arena.

"But clearly there's a lot of unhappiness inside Yemen. And I think we will basically just continue to watch the situation." Asked if the US government was anticipating Saleh's downfall, Gates said: "We haven't done any post-Saleh planning, if you will." Yemen's parliament on Wednesday approved a state of emergency declared by Saleh despite an appeal from young Yemenis that it could trigger a new "massacre" aimed at quelling their anti-regime protests. Saleh has ruled for more than three decades but now faces an escalating campaign for his removal.