TEHRAN, July 12 (Xinhua) -- Iran on Thursday denied allegations by the British navy that the Iranian naval forces intended to stop a British oil tanker in the country's southern waters, amid calls for de-escalation of the Persian Gulf tensions.

Earlier on Thursday, Britain's Ministry of Defense said that Iranian boats tried to impede the passage of a British oil tanker near the Gulf, before being driven off by a Royal Navy ship.

"The IRGC's Navy vessels carry out their regular patrolling missions in the Gulf ... In the past 24 hours, there has been no encounter with foreign ships, including British ones," Iran's Islamic Revolution Guards Corps (IRGC) responded in a statement.

According to media reports last week, British Royal Marines in the Strait of Gibraltar seized an Iranian ship which was heading to Syria "in breach of European Union (EU) sanctions."

Britain's allegations were made one day after Iranian President Hassan Rouhani warned of "consequences" for Britain's seizure of the Iranian ship which according to the Spanish Acting Foreign Minister Josep Borrell was at the U.S. request.

Also on Thursday, the U.S. State Department condemned Iran's IRGC navy for trying to "unlawfully harass and interfere with" the passage of the Britain-flagged merchant vessel.

Amid the quarrel between Iran and Britain over the alleged seizure of oil tankers, U.S. President Donald Trump on Wednesday repeated his threat to increase sanctions against Tehran. "Sanctions will soon be increased, substantially!" he tweeted.

Tensions shrouding the region have been escalating recently. Last month two oil tankers were hit in the Gulf of Oman. The United States and Britain have accused Iran of being responsible for the attacks, which Tehran denied.

Such a worsening situation has raised calls for de-escalation of the Persian Gulf tensions.

Russia on Thursday calls on the United Nations (UN) to play a more active role in easing tensions in the region.

"We advocate increasing the United Nations' profile in implementing mediation-based diplomacy," Russian Deputy Permanent Representative to the UN Vladimir Safronkov said.

Earlier this week, Chinese Foreign Ministry Spokesman Geng Shuang at a press conference called on relevant parties to "remain calm and exercise restraint."

"They should take concrete measures to prevent escalation and jointly safeguard peace and stability in the region," Geng said, noting that "it serves the interests of the Gulf and also the wider world."