(Update with doctor's release)
ADEN, Yemen, Feb 22 (Reuters) - A Czech doctor was freed several hours after being kidnapped by gunmen in the Yemeni capital Sanaa, security sources said.
The doctor was walking to work at a private hospital when the armed assailants blocked her way with their car and seized her, the sources said. She was the third foreigner to be snatched this month.
Security sources said on Sunday the kidnappers later freed the woman unharmed, leaving her on a main road east of the capital, and that she returned home on her own. The reasons for the kidnapping and the release were not immediately clear.
The incident highlighted the increasing breakdown of security in the U.S.-allied country, which is struggling to restore state authority weakened since mass unrest in 2011 that forced long-serving President Ali Abdullah Saleh to step down.
The kidnapping followed the abduction of a British oil worker by unidentified gunmen and a German seized by Yemeni tribesman to press for the release of their jailed relatives.
An intelligence officer, Colonel Ahmed Hashem, was shot dead on Saturday by suspected al Qaeda militants in Atek in the southern province of Shabwa, a security source said.
Yemen, which neighbours oil giant Saudi Arabia and is home to an active al Qaeda offshoot, has long wrestled with instability, internal conflicts and poor governance.
Apart from kidnappings, Yemen is struggling with a rebellion by Shi'ite Muslims in the north, a secessionist movement in the south and attacks by al Qaeda-linked militants. (Reporting By Mohammed Mukhashaf; Writing by Maha El Dahan; Editing by Mark Heinrich)