Yemen says it has foiled an al-Qaeda plot to blow up oil pipelines and seize some of the country's main ports.
Security remains tight - and hundreds of armoured vehicles have been deployed to protect key targets.
Both the United States and the United Kingdom have withdrawn diplomatic staff from Yemen, prompted by intelligence reports of renewed terrorist activity.
The US is reported to be preparing special operations forces for possible strikes against al-Qaeda in Yemen.
The BBC reports it appears that Yemen was at the centre of a complex and audacious plot which - had it succeeded - would have given al-Qaeda control over a crucial aspect of the country's infrastructure.
Yemeni government spokesman Rajeh Badi said the plot involved blowing up oil pipelines and taking control of certain cities on the 27th day of Ramadan, which has recently passed. They included two ports in the south, one of which accounts for the bulk of Yemen's oil exports and is where a number of foreign workers are employed.
"There were attempts to control key cities in Yemen like Mukala and Bawzeer," Mr Badi said. "This would be co-ordinated with attacks by al-Qaeda members on the gas facilities in Shebwa city and the blowing up of the gas pipe in Belhaf city."
Al-Qaeda members dressed as soldiers were to be outside the ports, he said. On a given signal they were to invade the facility and take it over.
Meanwhile, Yemen has criticised the withdrawal of diplomats, saying it served the interests of extremists.
The US embassy and consulate closures reportedly followed intercepted conversations between two senior al-Qaeda figures, including top leader Ayman al-Zawahiri, suggesting renewed terrorist attacks.
The decision to withdraw the diplomats was made after a drone strike that US officials have confirmed killed four al-Qaeda suspects in Yemen.