The embassy said on its website that Yemeni security forces had addressed a "specific area of concern" in the north of the capital on Monday, paving the way for Tuesday's reopening.
Warnings of a possible Al-Qaeda attack had led Washington to close its embassy in the Yemeni capital on Sunday. The British and French authorities followed suit, while Japan suspended consular services at its embassy.
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There was no sign on Tuesday that the other missions had resumed normal operations.
"Successful counter-terrorism operations conducted by the government of Yemen security forces January 4 north of the capital have addressed a specific area of concern, and have contributed to the embassy's decision to resume operations," it said.
The statement appeared also to refer to a security operation conducted by Yemeni police Monday in the area of Arhab, 40 kilometres (25 miles) north of Sanaa, where two suspected members of Al-Qaeda were killed and three others wounded.
"The United States commends the government of Yemen for its efforts to disrupt Al Qaeda in the Arabian Peninsula (AQAP) networks, and reiterates its commitment to continue to support these efforts," it added.
The statement was referring to Al-Qaeda's franchise in Yemen which claimed responsibility for the failed attack on a US airliner on Christmas Day, and urged attacks on Western interests in the country.
The Yemen interior ministry said Tuesday that all foreign missions and interests were "safe" pointing out that it has reinforced security measures around embassies and residents of foreigners.
The ministry also said that is arrested five "terrorist elements" over the past two days near the capital, but gave no details.
The culprit of the botched attack on the Northwest Airlines flight from Amsterdam to Detroit, Umar Farouk Abdulmutallab, 23, has reportedly confessed to being trained by an Al-Qaeda bombmaker in Yemen for his suicide mission.
US President Barack Obama has revealed that Abdulmutallab spent time in Yemen during the summer where he was allegedly in contact with AQAP.
US Secretary of State Hillary Clinton had on Monday said Washington would reopen its mission in Yemen "when the conditions permit."
"The instability in Yemen is a threat to regional stability and even global stability," Clinton told reporters in Washington following talks with Qatari Prime Minister Sheikh Hamad bin Jassem bin Jabr al-Thani.
"And certainly, we know that this is a difficult set of challenges, but they have to be addressed," Clinton said.
Speaking on a visit to Qatar, Yemeni Foreign Minister Abu Bakr al-Kurbi said on Monday that his country needed help to take on the militants who have found the impoverished Arabian Peninsula country a fertile ground for recruitment.
"Certainly there is a problem with Al-Qaeda and an interest among the international community in its activities," Kurbi said.
"Yemen is capable of confronting these groups, but it needs international aid to form and train anti-terrorist units as well as economic aid, since the problem also has an economic dimension."
Obama's counter-terrorism adviser John Brennan said on Sunday that Washington was making a "determined and concerted effort" to help fund Yemen's special Counter-Terrorism Unit.
At the same time, US officials said Yemen was one of 14 "terror linked" countries to which enhanced airline passenger screening would be applied. Cuba, Iran, Sudan, Syria Afghanistan, Libya, Nigeria, Pakistan and Somalia are among some of the other countries affected.
The new designation means that all passengers flying into the United States from the countries will be subject to measures such as body pat-downs and searches of their hand luggage.
