(CNN) -- The U.S. Embassy in Yemen, which was closed over the weekend due to security concerns, reopened Tuesday.
A statement posted on the embassy's Web site said that "successful counter-terrorism operations" conducted by Yemeni security forces had addressed specific concerns.
"Nevertheless, the threat of terrorist attacks against American interests remains high and the Embassy continues to urge its citizens in Yemen to be vigilant and take prudent security measures," the statement said.
A senior State Department official, who did not want to speak on the record due to the sensitive nature of the information, said Yemeni authorities have helped the United States with additional security precautions at the embassy site.
Yemen fertile ground for terror groups
The United States' decision to close its embassy in Yemen came after intelligence suggested that four al Qaeda operatives may be planning an attack on the compound, a senior administration official said Monday.
The United States had information that a group of eight terrorists had been planning an attack, the official said. Three were killed by Yemeni forces in recent days and another was captured wearing a suicide vest, but the other four were believed to be at large, the official said.
Earlier Monday, Secretary of State Hillary Clinton called the situation in Yemen a possible threat to regional and global security. However, Clinton commended Yemen for taking action against al Qaeda networks and added: "We are reiterating our commitment to assist in those efforts."
The United States and Britain closed their embassies Sunday. Britain's Foreign Office also cited security concerns and remained closed on Tuesday.
"The British Embassy in Yemen will remain closed to the public today," a statement from the embassy said. "Some embassy personnel will be in and whoever needs to contact the embassy can do it via the phone or email but people won't be able to walk into the embassy."
Several other nations also made changes at their embassies Monday, including Japan, France, Spain and Germany. Each country cited the need for increased security measures.
France closed its embassy to the public. French Foreign Ministry spokesman Bernard Valero said Tuesday that embassy employees will continue their work, but without any visits from the public.
Valero said the embassy will reopen once work to secure the site, already in progress before the latest threat, has been finished.
Japan halted service at the consulate section of its embassy in Sanaa. The Japanese Foreign Ministry said the decision was based on the threat of terror, though not a specific threat. The embassy continued functioning.
Spain restricted public access to its embassy, the Spanish Foreign Ministry said, adding that the embassy continued to function "normally."
Germany said that while its embassy remained fully operational, security measures were increased. A spokesman for the German Foreign Ministry said fewer visitors were allowed into the embassy compound. The embassy had not received any terror threats, the spokesman said.
The wave of concerns was triggered by last month's attempted terrorist attack on a U.S.-bound airliner. Yemen-based al Qaeda in the Arabian Peninsula claimed responsibility. On Saturday, U.S. President Barack Obama linked the Nigerian suspect, 23-year-old Umar Farouk AbdulMutallab, to the group, which is a combination of al Qaeda networks in Saudi Arabia and Yemen.
The U.S. Embassy in Yemen has come under attack numerous times in recent years. In September 2008, 10 people were killed -- among them police and civilians, but no embassy employees -- when insurgents opened fire and set off explosions outside the compound.
The U.S. Embassy last week, on December 31, notified Americans in Yemen to remain on alert for the possibility of terrorist violence.
"I think what we've seen over the past several years in Yemen is an increasing strengthening of al Qaeda forces in Yemen," John Brennan, assistant to the president for homeland security and counterterrorism, told CNN. "There are several hundred al Qaeda members there."
Al Qaeda in the Arabian Peninsula said the attempted Christmas Day attack onboard a Northwest Airlines flight from Amsterdam, Netherlands, to Detroit, Michigan was in retaliation for airstrikes against it on December 17 and 24.
