President Barack Obama's aide John Brennan called the Yemeni leader to urge him to sign and implement the agreement "so that Yemen is able to move forward immediately with its political transition," a White House statement said.
An aide to the embattled Yemeni president said the nation's political rivals had agreed to sign the plan brokered by the region's six-nation Gulf Cooperation Council today.
But parliamentary opposition spokesman Mohammed Qahtan said Saleh had backed out of signing the accord, which would see Saleh out of office within 30 days.
"We came to an agreement late Tuesday but this morning they changed their minds," Qahtan told AFP, adding Saleh and his partisans "refuse" to sign it this way.
According to the US statement, Brennan "noted that this transfer of power represents the best path forward for Yemen to become a more secure, unified, and prosperous nation and for the Yemeni people to realize their aspirations for peace and political reform."
He also affirmed the commitment of the United States to stand with the Yemeni government and people as they implement this historic agreement, foster economic development, and combat the security threat from Al-Qaeda in the Arabian Peninsula.
Brennan "reiterated that all parties must refrain from violence and proceed with the transition in a peaceful and orderly manner," the statement said.
On the ground, most of Yemen's cities observed a complete strike on Wednesday morning as police fired shots into the the air in the town of Huta, in southern Lahij province, and in the Red Sea city of Al-Hudaydah, witnesses said.
Massive protests took place in Taez and Ibb, south of Sanaa, and Al-Hudaydah, according to witnesses. In Huta, where protesters blocked roads, residents said police fired into the air.
Yemen's southern cities of Aden, Lahij and Shabwa also went on strike today, according to residents there.
The impoverished but strategic Arabian Peninsula country has been gripped by protests since late January calling for the ouster of Saleh, who has been in power since 1978.
Security forces launched a deadly crackdown the protests, leaving at least 180 people dead, according to a toll compiled from reports by activists and medics.