Syria's president, Bashar al-Assad, has said there is no immediate prospect of an end to the country's 17-month-old civil war, adding that more time is needed for his "heroic" armed forces to wipe out the opposition.

In an interview with Syria's pro-government Addounia TV channel, Assad shrugged off recent damaging defections by senior regime figures, and suggested the situation for ordinary Syrians was now gradually improving. Events on the ground on Wednesday, however, suggested otherwise, with heavy shelling near the capital Damascus and a major rebel attack on a strategic northern airbase.

"We are moving forward, the situation is practically getting better, but the victory needs more time," Assad said. He continued: "We're fighting a regional and global battle and must have more time to resolve [it]."

The interview marks a rare public appearance for Assad, and follows a devastating explosion last month at his Damascus military-security command, which killed four of his top advisers. Assad laughed off claims that he had fled the capital, or escaped abroad, telling his interviewer: "I'm here with you in Damascus inside the republican palace."

The president also praised his country's embattled armed forces. Opposition activists and human rights groups accuse Assad's troops and pro-government shabiha militias of staging a series of massacres, most recently in the town of Daraya. Up to 400 people were reportedly killed there over the weekend. "The army are doing their job. They are performing heroic acts in every sense of the word," Assad said.

Assad also suggested outside diplomatic pressure to end the conflict made little difference, and said he did not think a no-fly zone over Syria would ever happen. "The truth is that Syria doesn't need a green light when dealing with its internal affairs, neither from our allies or our enemies," he told the channel, owned by his cousin Rami Makhlouf, one of Syria's wealthiest men.

Assad's remarks, showing him to be relaxed and calm, came as his new prime minister, Wael Nader al-Halqi, arrived in Tehran for a two-day summit. Iran, Assad's principal regional backer, proposed a three-month ceasefire inside Syria. The UN secretary general, Ban Ki-moon, also attended the non-aligned summit, with Egypt's new president, Mohamed Morsi, due to drop in on Thursday.

But the Iranian initiative has little prospect of success and came amid another day of carnage across Syria. Residents in Ghouta, three miles (5km) east of Damascus, said they had been under bombardment from government tanks and warplanes for two days. "A lot of people are fleeing Ghouta to escape the random shooting, but they don't know where to go," one resident, Abu Omer, told the Guardian via Skype.

Omer said the regime had punished the area – home to two million people – after fighters from the Free Syrian Army (FSA) shot down a warplane. He said the Syrian army was now converging in nearby Ain Terma and al-Miliha, and was attempting to storm the town. "There are conveys of tanks and armoured vehicles full of soldiers on the highway that divides Damascus and eastern Ghouta. The snipers are shooting anyone in sight," he said. The regime had forced local bakeries to close, with food and medicines now in short supply, and was shooting civilians sheltering in their houses. The victims included two children in Juber aged seven and eight, and three women, he said.

Omer's claims are impossible to verify. But video footage posted on YouTube on Wednesday appears to show heavy bombardment of Ghouta, with residential buildings targeted next to a minaret and smoke billowing across the skyline. More than 40 people have been killed by pro-regime militias in outlying areas, activists said.

In northern Syria, an armed Islamist rebel group claimed it had carried out a major attack on the Taftanaz airbase near the town of Idlib. At least five helicopters were destroyed, it said, with the rebels assaulting the airbase using tanks captured from a Syrian military checkpoint and rocket-propelled grenades.

"The operation lasted for 40 minutes," one rebel commander, Tamiem al-Shami, told the Guardian via Skype. "We were able to take out most of the defences at the base. We used a lot of fire against the helicopters and could see with our own eyes how the helicopters were burning." Shami said he was a member of the Ahrar al-Sham brigade in Idlib, an Islamic religious unit which was separate from the FSA but co-operated with it.

Shami said three of his men were killed during the operation and one injured. The rebels withdrew when Syrian warplanes attacked their positions, he added. The Syrian state news agency Sana said forces loyal to the government had successfully repulsed the assault.

Turkey's foreign minister, Ahmet Davutoglu, meanwhile, said he would press the UN security council to set up a safe haven inside Syria to protect thousands of people fleeing the violence.

Turkey has long been floating the idea of a no-fly zone, or buffer zone, to protect displaced Syrians from attacks by Assad's forces, but the issue has become more pressing now the number of refugees in Turkey has exceeded 80,000 – a number it says approaches its limits. "We expect the UN to step in and protect the refugees inside Syria, and if possible, to shelter them in camps there," Davutoglu told reporters before leaving for New York to attend Thursday's high-level UN security council meeting on Syria.