Sanaa, Yemen (CNN) -- Yemen foiled an al Qaeda plot to capture oil and gas facilities and seize two key southern ports early this week, a spokesman for the prime minister said Wednesday.

However, another Yemeni government official said it did not appear that the plot was the terror threat that prompted the United States on Tuesday to urge Americans to leave the country.

That official, who was not authorized to speak to the media, downplayed the report of the plot disruption, saying that "these are ongoing threats to oil and gas installations in Yemen."

Al Qaeda in the Arabian Peninsula "has neither the manpower nor the capabilities to capture ports or seize pipelines," the official said. "Security precautions are always in place regarding all oil installations and energy infrastructure in Yemen."

News of the foiled plot comes after the United States, acting on intelligence information, issued a worldwide travel alert and closed a number of embassies and consulates over large areas of the Middle East and Africa this week.

Rajeh Badi, a spokesman for Yemen's prime minister, said that Yemen "ended an al Qaeda plot to attack strategic locations in Mukalla and Shabwa," referring to a Yemeni port city and a southern province.

"Large numbers of government forces are making sure the Yemeni coasts are safe from any al Qaeda attack. Al Qaeda sought to attack the oil pipelines, but failed and tried to attack through the coast of Mukalla but failed as well," he said.

However, the state news agency Saba denied there was ever an al Qaeda plot to take over Mukalla. It cited a security source it did not name.

U.S. State Department spokeswoman Jen Psaki told reporters Wednesday that the U.S. Embassy there remains closed "because we believe that a threat remains."

On Tuesday, two U.S. military transport aircraft landed in Yemen to evacuate American citizens. The UK Foreign Office has also withdrawn its embassy staff.

A senior Yemeni Interior Ministry official told CNN that "a few" al Qaeda operatives arrived in Sanaa over the past three days, which has forced government authorities to put Yemeni forces on high alert. The official could not be named, as he is not authorized to speak to the media.

"We are confident that government security forces will be able to stop any attack from taking place in Sanaa, but the militants do have a good history of operating in Sanaa," he said Tuesday.

"It's not a secret that al Qaeda also has sleeper cells in Sanaa," the source said.

Bergen: What's behind timing of terror threat

Evacuation troubles Yemen ministry

Psaki said Tuesday that the United States has "a close partnership" with Yemen and that Secretary of State John Kerry had spoken with President Abdu Rabu Mansour Hadi to thank him for his efforts.

But in a sign of possible tensions with its international allies, Yemen's Ministry of Foreign Affairs said the evacuation of embassies "serves the interests of the extremists" and undermined its efforts.

List of U.S. embassies and consulates closed this week

"Yemen has taken all necessary precautions to ensure the safety and security of foreign missions in the capital Sanaa," a statement said Tuesday.

"While the government of Yemen appreciates foreign governments' concern for the safety of their citizens, the evacuation of embassy staff serves the interests of the extremists and undermines the exceptional cooperation between Yemen and the international alliance against terrorism."

Meanwhile, Sanaa residents told CNN of their concern about long-term security issues and fears of possible U.S. intervention in Yemen.

University student Sara al-Shibani said she felt Yemen had no option but to concede to "international powers," since the country is weak and poor. She also worries that "many Yemenis will die because of ... foreign involvement in Yemeni politics."

"The United States is making Yemenis feel that we are ... the next Afghanistan," said local banker Nasser al-Maqdashi.

Drone strikes kill 6; helicopter shot down

Six militants in separate vehicles were killed in two drone strikes in Shabwa province Wednesday morning, according to several official sources in Yemen not authorized to be named.

This was the fifth such strike in two weeks, and the second in Shabwa. A local security official, speaking on condition of anonymity, told CNN that he does not believe any of those killed were senior al-Qaeda members.

The latest strikes came a day after a pair of suspected U.S. drone strikes killed four al Qaeda militants in Yemen. Security sources told CNN about those strikes but didn't offer additional details. None of those killed Tuesday were among the 25 names on the country's most-wanted list, security officials said.

It was unclear whether Tuesday's strikes were related to the security alert in place in the country since U.S. officials intercepted a message from al Qaeda leader Ayman al-Zawahiri to operatives in Yemen telling them to "do something."

The message was sent to Nasir al-Wuhayshi, the leader of AQAP, the terror group's Yemeni affiliate. U.S. intelligence believes al-Wuhayshi has recently been appointed the overall terror organization's No. 2 leader.

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Three sources told CNN that the United States has information that members of AQAP are in the final stages of planning for an unspecified attack. Recent jailbreaks in Pakistan, Iraq and Libya all have the fingerprints of al Qaeda operations.

Meanwhile, a Yemeni government official not authorized to speak to media told CNN that a Yemeni military helicopter was shot down in Mareb province Tuesday.

He said that the helicopter had been inspecting the country's main oil pipeline -- one that has been subject to repeated attacks -- and added Wednesday that "AQAP is now the prime suspect."

At least eight people were killed, including the 107th Brigade commander, six army escorts and at least one crew member, he said.

AQAP's recent attacks have included a suicide bombing on a pro-government militia in the south in March that killed 12, and an attempted suicide bombing attack on a gas pumping facility in the port city of Balhaf in June.

In July, several soldiers were killed by a bomb in Sanaa after a lull in attacks in the capital.

AQAP has not mounted a large-scale suicide attack on Yemen's security forces since May 2012, when more than 100 soldiers were killed by a suicide bomber as they trained for a parade in Sanaa.

Many of AQAP's operatives, including its leadership, retreated into remote areas after the Yemeni military offensive last year and regrouped.

The Yemeni security forces, extensively reorganized under Hadi, have over the past 18 months recaptured swathes of territory that were briefly held by AQAP, particularly in the south of the country.

CNN's Mohammed Jamjoom reported from Beirut and journalist Hakim Almasmari from Sanaa, while Laura Smith-Spark wrote in London. CNN's Elise Labott, Barbara Starr, Tim Lister and Paul Cruickshank contributed to this report.