South Yemen separatists say they are economically marginalized
Suspected al-Qaeda militants in north Yemen have killed five security force members, three of them senior officers.
The security men were ambushed as they travelled back from a post on the border with Saudi Arabia.
A local official said the attack had been carried out by "elements linked to al-Qaeda" who are "active in the area", the Reuters news agency reported.
Al-Qaeda said in January 2009 that its Yemeni and Saudi branches had merged to broaden attacks in the region.
The latest ambush happened in the eastern province of Hadhramut, according to the AFP news agency.
It quoted an official source naming two of the senior staff as Brig Gen Ali Salem al-Ameri, security chief of the area, and state security official Ahmed Bawazeir.
Western countries and their allies in the Middle East fear al-Qaeda's influence is growing in Yemen amid increasing instability.
The government is trying to contain several rebel groups in Yemen.
There are the Shia Houthi rebels in the north and a secessionist movement in the south.
And Saudi Arabia says many of its wanted militants are sheltering in Yemen.
On Monday, Saudi officials said they had found a weapons cache they believed was linked to the merged al-Qaeda entity, al-Qaeda in the Arabian Peninsula.
The conflict against the Houthis has intensified since the army launched a fresh offensive in August 2009.
The Houthi rebels have long accused Riyadh of supporting the Yemeni government in attacks against them.
In October 2009 there were clashes between Houthis and Saudi security forces near the border.
Yemen is one of the world's poorest countries and analysts question the ability of the government to assert control over the country.