Russian drones have struck at least a dozen merchant ships in the Black Sea in recent weeks – killing more mariners than have died during the Iran war.

Russia’s goal is to throttle trade through Ukrainian ports, which export almost all the country’s grain. But some attacks have occurred close to or inside the territorial waters of two NATO states: Romania and Bulgaria.

The Russian campaign follows months of Ukrainian strikes on ships using Russian ports in the Black Sea and adjoining Sea of Azov – and has accelerated over the past month.

On several occasions, according to shipping and security sources, Russia has combined maritime and aerial drones. It has begun using recently developed jet-powered drones, which are faster and more difficult to intercept, as well as drones capable of hitting moving targets.

Altogether, at least 30 mariners have been killed or are missing in the recent surge of attacks, according to maritime tracking services and the governments of Romania and Bulgaria.

In the most recent strike, three drones struck a container ship last week as it approached a Romanian port. A French surveillance plane filmed a surface drone zeroing in on the vessel – the Contship Jet – and later video showed the ship listing heavily before sinking. When hit, the vessel was just 25 kilometers (15 miles) from the Bulgarian coast.

Ukrainian Foreign Minister Andrii Sybiha has said that the uptick in attacks is “turning the Black Sea into a zone of danger for civilian shipping.”Russia increased missile and drone attacks on Ukrainian Black Sea ports, particularly Odesa, over the summer. Ukraine exported 1.09 million tons of wheat in September, half the 2.05 million tons a year earlier, according to government figures. The Ukrainians tried to divert exports to smaller ports on the Danube River – which borders Romania – and Russian drones followed.

The surge in attacks began in early October, when the Turkish-owned Alfa Watan, heading from Egypt to the Romanian port of Sulina, was struck by air and naval drones. Nine Syrian crew members and one Egyptian died, and the ship sank.

Six days later, 11 of the crew on the HS Dignity – most of them Syrian – died when the ship was struck off the Bulgarian coast at night.

A Syrian seafarers’ activist, Mohammad Hajjouz, told CNN that after the first strike on the Dignity, the crew saw an unmanned surface vessel approaching, which then struck the ship. Unable to fully launch the lifeboats, crew members jumped in the water.

“They began calling out to one another and trying to regroup, but the sea was rough and the water was extremely cold, causing crew members to drift apart,” Hajjouz said. Despite the growing danger, some shipping firms are still working in the Black Sea.

“Economic hardship pushes sailors to accept work in dangerous areas. They are sometimes enticed by offers of additional pay,” Hajjouz said. “Others are compelled to work in these areas due to limited employment opportunities.”On October 15, four more merchant ships were targeted, “including in Romanian territorial waters and its economic exclusive zone, and eight lives were lost,” according to Romanian Foreign Minister Oana-Silvia Toiu.

Two chemical tankers – Wine Trader and Yara J – caught fire after being hit close to the Sulina Canal that leads from the Black Sea into the Danube.

Six Beninese and one Russian national on the Wine Trader, which was hit by three drones according to its operator, were killed.

“Russian forces are striking vessels linked to Ukrainian trade, now inside the (exclusive economic zones) of two NATO member states,” according to maritime analysts at Ambrey, a shipping intelligence firm“Romanian and Bulgarian waters should no longer be treated as safe by default,” Ambrey added, saying several vessels were very likely targeted due to their Ukrainian grain export links.

Moscow has not acknowledged all the attacks, but in several instances the Russian Ministry of Defense claimed that targeted vessels were carrying “military and dual-use cargo” for the Ukrainian armed forces.

The European response has been fragmented. NATO Secretary General Mark Rutte said the alliance has “already strengthened our posture along the eastern flank,” as Russian attacks encroach on the alliance’s borders.

The Bulgarian government, which has relatively good relations with Moscow, has been reluctant to blame Russia, but there are now signs that it and Romania are mobilizing defenses.

Bulgaria has asked NATO to deploy combat aircraft and anti-drone systems to bolster its defenses, according to Defense Minister Dimitar Stoyanov, who also expects Bulgaria to join a NATO anti-drone initiative.

The Romanians have begun deploying patrols of F-16 jets along the coast. One of them shot down two of the latest generation of Russian drones over Romanian territorial waters in late October.

Romania has also said it will accelerate the development of surveillance capabilities and equipment to counter mines and drones in the Black Sea.

But the moves have not done enough to reassure shippers. Traffic visiting Ukrainian ports has fallen sharply, while insurance rates have spiked.

Last month, the Joint War Committee, which assesses risk for the London insurance market, extended the areas defined as “high-risk” to include the whole of the Black Sea region, excluding the territorial waters of Turkey, Romania, Bulgaria and Georgia.

Higher premiums are bad news for Ukraine’s vital agriculture exports, 90% of which transit the waterway. Ukraine supplies about 15% of global maize exports and 10% of wheat, and is the world’s top exporter of sunflower oil.

German Foreign Minister Johann Wadephul has described the Black Sea as vital for global food security. But Russia “has put freedom of navigation in the Black Sea, and with it a lifeline for so many people, in its crosshairs,” he said last month. For its part, the Trump administration has blamed both sides for the shipping attacks.

“We have American companies calling us and saying, ‘Hey, that was our oil on that ship that was hit by Ukraine,’” US Secretary of State Marco Rubio said last month. “Now, I don’t believe Ukraine intentionally targeted them, but those ships got hit,” he added.

NATO and the Black Sea states must “develop anti-drone defenses, and the Alliance should beef up its presence in Romanian and Bulgarian airspace and on land,” according to Dimitar Bechev, director of the Dahrendorf Programme at St Antony’s College at Oxford.

“At sea, Turkey, Romania and Bulgaria could do more to enforce freedom of navigation,” Bechev told CNN.

Ukraine and Russia are punishing each other without gaining any kind of lasting advantage, according to David Axe, author of the Trench Art blog on the conflict in Ukraine. That has left much of the Black Sea very perilous for commercial vessels.