Though they still lack the kind of heavy weaponry that might help them decisively drive back the military, rebels in central Syria are constructing bigger and more effective bombs, and a steady flow of money from the militants’ leadership in Turkey has allowed them to purchase sufficient amounts of small arms.

Some groups have said recently that they have an increased number of modern anti-tank rockets, and others say they’re manufacturing so-called explosively formed penetrators to increase the killing power of their roadside bombs. EFPs, cone-shaped copper plates that are blasted into vehicles when the bombs explode, wreaked havoc on U.S. vehicles in Iraq.

“They are hard to get and expensive,” complained Abu Omar, a 25-year-old former university student who spends his days making bombs with fertilizer, mostly by packing it into empty cooking-gas containers. Syrian state-run news agencies routinely have reported seizures of such materials in past months across the country. For targeting tanks, he packs truck axles cut in half full of explosives, he said.

Members of the armed opposition say the more sophisticated weapons are being transported across the border from Turkey with the knowledge of the Turkish intelligence service, an allegation Turkey has previously denied.

The improved supply of weapons to the rebels is clearly evident, both to reporters traveling in rebel-held area and in the rising death toll among Syrian security forces in clashes with the rebels. On Wednesday, the Syrian government announced the funerals of another 27 soldiers and police officers who died in clashes with the rebels, bringing to 322 the number of such deaths so far in June. Rebel casualties are uncertain, but in the same time period the Syrian Network for Human Rights has published daily tallies of 751 deaths it attributed to pro-government forces, including 78 at Qubeir who allegedly were killed by local militia known as shabiha.

Many rebel commanders in this part of Syria, where rebel units can travel largely without encountering military forces, didn’t want to address the subject of increased arms supplies, fearing that admitting they’re better armed and funded than before might make the world less sympathetic to their cause. The would-be revolutionaries have gone to lengths to paint themselves as the victims in what’s become an all-out civil war.

But they hint at arms shipments. A Turkish-speaking Syrian who arrived in Khan Sheikhoun earlier this week to drop off communications equipment acknowledged the arrival of more sophisticated weapons, but he wouldn’t say exactly what they were.

“It’s a surprise. Just wait,” the man said, smiling and promising that the rebels would be going on the offensive in coming weeks. Other commanders in the area have said the same.

The promise of a rebel offensive also carries the promise of more destruction and displacement. According to the Turkish government, about 4,000 Syrian refugees have crossed into Turkey in the last week, bringing the number of Syrians taking refuge in seven camps just inside the Turkish border to nearly 30,000. The cramped camps have become training grounds for the rebels, who share expertise with one another before slipping back across the border.

Much of the rebels’ improved firepower appears to come from local innovation.

“Before the revolution, I worked with electronics,” said Isam al Hamadee, the leader of a group of fighters from the town of Kefar Nbouda who’s become well known among local rebels for his expertise in building remotely detonated bombs.

The rebels also are manufacturing their own rockets, including remote-controlled anti-aircraft and anti-tank rockets.

But for some groups, the lack of heavy weapons has prompted a shift to more extreme tactics.

Ahrar al Sham, a group that coordinates with the rebels who operate under the name Free Syrian Army but isn’t directly under its leadership, carried out a suicide bombing against a checkpoint near this battered city last Thursday.

The leader of the group here, who uses the nom-de-guerre Abu Hamza, said the bombing was the first of its kind that his group had carried out, though other branches of Ahrar al Sham, which has proliferated across north-central Syria, had done so.

Members of Ahrar al Sham said the bomber was a 19-year-old man from Khan Sheikhoun who’d been present when Syrian soldiers fired on a group of demonstrators in the city last month, killing a number of them. The man, who took the nom-de-guerre Abu Abdullah, had seen one of his friends die.

“Of course some of the people had reservations,” Abu Hamza said. “But Abu Abdullah wanted to do this. He put it in his mind and couldn’t sleep.”

“It is better to die this way rather than be slaughtered like the people in Houla,” Abu Hamza said, referring to the 80 women and children who were killed last month, allegedly by supporters of the government of President Bashar Assad. “These operations will continue if the world doesn’t give us weapons. We have more people ready to do this.”

“What would you do if the government was killing your family? Your children?” asked one rebel who’d gathered with hundreds of others to watch smoke rise from the massive bombing. “We don’t have heavy weapons, and they have tanks and helicopters.”

Rebels frequently express concern that they’ll be seen as terrorists in the West, sometimes joking with reporters, sometimes serious. It was the selection of a military checkpoint as the target for the bombing that was the issue, not the tactic of a suicide bombing itself.

“We don’t care what the outside world thinks,” another member of Ahrar al Sham said, when he was asked whether such bombings might be seen as counterproductive to their cause.

Syrian and international media didn’t report the bombing, which engulfed the checkpoint in smoke. It’s unclear how many people were killed and whether any civilians died in the blast.