Yemeni authorities have uncovered at least 13 al-Qa'ida plots to target foreign diplomats, embassies and senior military and government officials in the capital of Sanaa and other cities, a high ranking security official said.
The official said authorities were tipped off by captured al-Qa'ida members.
He said they gave information about sleeper cells plotting a string of assassinations, bombings and abductions of foreign diplomats in the capital, as well as cities in troubled southern Yemen.
He said Yemeni president Abed Rabbo Mansour Hadi met top security officials to discuss the new information.
Al-Qa'ida is trying to hit back after a two-month Yemeni military offensive drove the militants out of several main strongholds in the south.
Al-Qa'ida took advantage of internal turmoil and a security vacuum to capture parts of southern Yemen during last year's uprising, when Yemenis took to the streets demanding ousting of long-time ruler Ali Abdullah Saleh.
Since he took power in February, Mr Hadi has worked on purging the Yemeni army of Saleh loyalists and regime members. At the same time he ordered an all-out offensive against al-Qa'ida in the south.
Yesterday, al-Qa'ida tried to seize the small town of al Awabel in al Dhali province, about 60 miles north of the southern port of Aden, according to military officials.
One soldier and one militant were killed in the fighting as troops backed by tribal gunmen repelled the militant assault. Nine al -Qa'ida-linked militants were captured.
The Yemeni offensive in the south is supported by US military advisers from a command centre manned by dozens of US troops in the al Annad air base near Abyan province, the main conflict zone.
The US considers al-Qa'ida's Yemen branch, known as al-Qa'ida in the Arabian Peninsula, to be the terror network's most dangerous offshoot.