"Continue the Change" (PP) and Romania's Save Romania Union party have asked NATO Secretary General Mark Rutte for stronger security in the Black Sea after drone attacks on merchant ships, PP's press office said.

This story follows our earlier report on Prime Minister Rumen Radev's call to the EU and NATO for joint action against attacks on ships in the Black Sea. On Wednesday he spoke by phone with Ursula von der Leyen and Mark Rutte and urged a united effort to stop the strikes on merchant ships.

The letter was signed by PP leader Asen Vasilev, Romanian party leader Dominic Fritz, and Renew Europe MEPs Nikola Minchev of PP and Dan Barna of Romania. Valérie Hayer, who leads the group in the European Parliament, also said she backed it.

The letter asks NATO to strengthen its joint military operations centre and its rotating command in the alliance countries that have a Black Sea coast. It says NATO must urgently assess what extra defence steps are possible: better maritime surveillance, counter-drone capabilities, and stronger air and missile defence. The aim is for Bulgaria, Romania and their allies to be ready for future threats.

On 6 October, sea and air drones hit two ships in Bulgaria's exclusive economic zone. On 13 October, drones struck two more ships in the Black Sea. The attacks took place close to the territorial waters of Bulgaria and Romania, and in the hours before the letter there were also strikes inside Romanian waters.

The authors say this is an escalation and a growing threat to Europe's security and to NATO's Eastern Flank. PP points to sunk ships, reports of missing crew members and endangered civilians, and says the threats call for immediate and firm action.

PP said the first data clearly point to Russian involvement.

"Europe's security starts at its borders," the two parties write. The letter says the Black Sea must be recognised as one of Europe's main security priorities.

The European Council and the European Parliament will discuss the worsening security in the Black Sea, and in the letter PP and the Romanian party welcome this decision.