Saleh however once again decided not to sign, and a brief but tense standoff occurred on 22 May when Saleh's supporters surrounded the embassy building of the United Arab Emirates in Sanaʽa, trapping international diplomats (including the secretary-general of the GCC) inside until the government dispatched a helicopter to ferry them to the presidential palace. On 23 May, a day after Saleh refused to sign the transition agreement, Sheikh Sadiq al-Ahmar, the head of the Hashid tribal federation, one of the most powerful tribes in the country, declared support for the opposition and his armed supporters came into conflict with loyalist security forces in the capital Sanaʽa after Saleh ordered al-Ahmar's arrest. Heavy street fighting ensued, which included artillery and mortar shelling. The militiamen had surrounded and blocked off several government buildings in the capital and people on the ground were reporting that it looked like the situation was deteriorating into a civil war. As the situation in Sanaʽa was developing, about 300 Islamist militants attacked and captured the coastal city of Zinjibar (population 20,000) (see Battle of Zinjibar). During the takeover of the town, the militants killed seven soldiers, including a colonel, and one civilian. Two more soldiers were killed in clashes with militants in Lawdar. On day three of the fighting, military units that defected to the opposition were hit for the first time by mortar fire killing three soldiers and wounding 10. By the evening, it was reported that tribesmen took control of the Interior Ministry building, SABA state news agency, and the national airline building. A ceasefire was announced late on 27 May, by al-Ahmar, and the next day, a truce was established. Opposition demonstrators had occupied the main square of Ta'izz since the start of the uprising against the rule of president Saleh. The protests were for the most part peaceful. However, that changed on 29 May, when the military started an operation to crush the protests and clear the demonstrators from their camp at the square. Troops reportedly fired live ammunition and from water cannons on the protesters, burned their tents and bulldozers ran over some of them. The opposition described the event as a massacre. (see 2011 Ta'izz clashes)  However, by 31 May, the ceasefire had broken down and street fighting continued in Sanaʽa. Tribesmen had taken control of both the headquarters of the ruling General People's Congress (Yemen) and the main offices of the water utility.