Yemen: Protesters seek action against al-Qaeda in Abyan
Thousands of Yemenis have rallied in the capital, Sanaa, demanding that the authorities do more to protect southern towns from being overrun by militants.
Al-Qaeda militants have reportedly besieged an army base in Zinjibar, Abyan province, amid reports of food and water shortages in the town.
At least 135 soldiers have been killed in clashes since late-May.
Yemen has been paralysed by five months of protests against President Ali Abdullah Saleh's 33-year rule.
Mr Saleh is in Saudi Arabia, being treated for burns and injuries sustained during an attack on his compound last month.
He has refused to cede power to his deputy, extending the political impasse in one of the Arab world's most impoverished and unstable countries.
On Monday, thousands of demonstrators marched towards the residence of Vice-President Abd-Rabbu Mansour Hadi in the capital Sanaa, demanding assistance for residents of Abyan province.
"We are against handing Abyan to elements of al-Qaeda," said one protester, Walid al-Amari.
"The people of Abyan are innocent," said Jihad al-Jafri, a female protester. "The vice-president and Yemeni officials are not doing anything."
Some chanted slogans that accused the authorities of "facilitating the takeover by al-Qaeda elements" in Zinjibar, the provincial capital.
Yemeni officials and journalists told BBC Arabic that militants from Ansar al-Sharia - a name used by leaders of al-Qaeda in the Arabian Peninsula (AQAP) - had surrounded the base of Yemen's 25th Mechanised Brigade on Sunday, and were trying to seize their equipment.
"[The soldiers] are in a critical situation, as they have run out of water and fuel, and they badly need military and logistic reinforcement in order to continue their resistance to the militants," Maj Abdullah Muthanna told the BBC during a telephone interview.
Sunday's standoff came after 50 soldiers from the brigade went "missing" after clashes on Wednesday. An army official said they still had no news of the men: "They could have been killed, captured or deserted during the fighting in the al-Wahda stadium," he told BBC Arabic.
Across Abyan province, residents have complained about severe fuel, food and water shortages.
With thousands fleeing to safety in Aden, there are fears that the violence could spread to the strategic oil port next.
The government has warned of a militant takeover in the south, but the opposition accuses the regime of exaggerating the threat to shore up Western support for President Saleh - a longtime ally in the US.
The 69-year-old leader, who has been in power since 1978, has not appeared in public since the 3 June blast at a mosque in the presidential compound that killed 11 people and wounded 124 others, among them senior officials.
In Mr Saleh's absence, protesters are demanding that Vice-President Hadi form an interim ruling council, but his grip on power is seen as shaky, as Mr Saleh's sons and relatives hold key security posts.