Ship carrying air defence systems and helicopters that was forced to return to port has been refitted with Russian flag

A Russian ship carrying attack helicopters that was prevented from sailing to Syria has been refitted with a Russian flag, rousing suspicions it is preparing for a second attempt.

The MV Alaed, carrying air defence systems and helicopters to Syria, was forced to return to port last week after its British insurers withdrew their coverage as the ship rounded the coast of Scotland. The Foreign Office and Treasury had warned the insurance company, Standard Club, that it could be in breach of sanctions against the regime of Bashar al-Assad if they allowed the ship to pass.

Sailing under the Curaçao flag, the ship returned on Sunday to the northern port of Murmansk, where it was "awaiting further instructions", the ship's owner, Femco, said in a statement. It said it would not comment on "the nature of the cargo on board".

The vague statement stood in stark contrast to official attempts to justify the weapons delivery.

Last week Russia's foreign minister, Sergei Lavrov, admitted that the Alaed was carrying supplies for Syria. "The ship was carrying air defence systems, which can be used only for repelling foreign aggression and not against peaceful demonstrators, and it was carrying three repaired helicopters," he told Ekho Mosvky radio.

Russia has repeatedly brushed off criticism of its continuing support for the Assad regime, insisting it was merely fulfilling long-agreed contracts in delivering supplies to Syria. Its role in arming Assad is likely to come under renewed scrutiny following the regime's downing of a Turkish jet at the weekend.

The shipments show no signs of stopping. An unidentified "military-diplomatic source" told the Interfax news agency on Sunday that the Alaed would soon travel from Murmansk to Syria in a second attempt to deliver the shipment. "The ship will travel under escort to avoid any sort of provocation," the source said. The escort ship would not be a naval one, the source added.

Femco made no mention of Syria in its statement, saying the ship's final destination was the far eastern port of Vladivostok. The ship would sail under the Russian flag "in order to protect its interests, the security of the ship and the protection of its crew, all of whom are citizens of Russia", it said.

Analysts said the flag change could up the stakes, threatening an international incident if any attempts were made to board it. Reports said the Russian flag was raised on Monday.

"We don't plan on justifying ourselves, because we haven't violated anything – not international law, not a UN security council resolution, not our own national laws on export controls, which are some of the strictest in the world," Lavrov said last week.

Syria is Russia's main remaining ally in the Middle East, a key weapons client and host to its base at Tartus, Russia's only military base outside the former Soviet Union.

An unidentified military source told Interfax last week that Russia was sending two warships to the base in case it needed to evacuate the thousands of Russian citizens living inside Syria.

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