(CNN) -- Fierce clashes followed suicide bombings and checkpoint attacks Sunday in Yemen, leaving dozens dead as the government fought back in a province largely controlled by terrorist groups, officials said.
At least 60 soldiers were killed in action, a Yemeni government official said, and the number of casualties was expected to climb.
Dozens of militants were killed, captured and injured, said the official, who asked to remain anonymous because he was not authorized to speak to the media.
Earlier Sunday, officials in the southern province of Abyan said 15 militants were killed in the clashes.
At least five troops were killed when suicide bombers earlier attacked two military posts in Abyan, where the government has been desperately trying to weaken terrorist groups after they took over large parts of the province last year.
The bombers used explosives-laden vehicles to hit posts on the outskirts of Zinjibar and in the town of Dofas, the officials said.
In a separate attack, militants killed four soldiers and wounded three others at a checkpoint in the town of al-Kod.
Residents said heavy clashes with militants erupted Saturday night in all three locations. Air raids were not enough to stop the militants from expanding and taking over two checkpoints in Dofas in addition to the three sites they attacked.
"The attacks were fierce against government forces. They used large amounts of heavy artillery, and this is not normal," said a senior security official in the province. The official is not authorized to talk to media and asked not to be named.
"Casualties are high from both sides, and this month will be decisive in our fighting against these militant groups," the official said.
Officials blame the attacks on Ansar al-Sharia, a group with links to al Qaeda in the Arabian Peninsula, the global terrorist network's branch in Yemen.
The attacks come less than a week after President Abdurabu Mansur Hadi took office and days after he changed top civilian, law enforcement and military officials in southern Yemen. The al Qaeda-linked attacks seem to be aimed at sending a message to the new administration, the Yemeni government official said.
Ansar al-Sharia fighters are also close to taking over the strategically important military base 115 on the outskirts of Zinjibar, the security officials said.
Clashes have been intense near the base since Saturday morning, with little resistance from the government or air support.
The site has been vital in the government attempts to uproot the militant group from the province since clashes started in May.
Witnesses told CNN that Ansar al-Sharia also cut off a main road linking the provinces of Abyan and Aden.
"Everyone who is traveling between the provinces would easily notice that al Qaeda is in control of the area," said Marwan Abdullah, a resident of Abyan who was heading toward Aden on Sunday.
Three senior security officials in Abyan accuse Mahdi Makwalah, the military commander of the southern regions, of handing over heavy artillery to al Qaeda fighters Sunday.
Last Thursday, Hadi issued a presidential decree ordering Makwalah to step down from his post, but the powerful military commander has so far refused to do so.
Among the weapons that al Qaeda fighters were given are nine tanks and heavy artillery, the officials told CNN.
"The only reason why al Qaeda is expanding in Abyan is because they are receiving aid from corrupt officials within the Yemeni government. This is the sad truth about the war on terror in Yemen," a security official in Abyan told CNN.
CNN's Jamie Crawford contributed to this report.