North Korea tried to export gas masks to Syria but they were seized in Turkey along with arms and ammunition, a Japanese daily said Tuesday, as the U.S. threatened action over an alleged chemical weapons attack.

A Libyan-registered vessel, identified as Al En Ti Sar, left North Korea for Syria earlier this year with the consignment, the Sankei Shimbun said, quoting unnamed sources from the US military, Japanese and South Korean intelligence.

The U.S. military, which obtained the information, was tracking the ship in coordination with other countries, the daily -- which is known for its North Korea coverage -- said in a detailed report.

The vessel sailed through Dardanelles in Turkey on April 3 and was searched shortly after by Turkish authorities, who had been tipped off by the U.S.

Turkish officials seized 1,400 rifles and pistols and some 30,000 bullets as well as gas masks apparently for chemical protection, the daily said.

U.S. authorities believe that the ship was intending to unload its cargo in Turkey and send it overland to President Bashar Assad's regime, the Sankei said.

Turkey detained the captain of the vessel and later charged him after he admitted his ship was on its way from North Korea and was carrying arms bound for Syria, the paper said.

Syria is the subject of sanctions by the European Union, the US and its allies banning the sale of weapons.

North Korea is barred by United Nations sanctions from trading in weaponry in the wake of nuclear and missile tests. If confirmed, Pyongyang could face additional U.N. sanctions over the shipment.

North Korea and Syria have reportedly had a military relationship for some years, including during the current civil war in the Middle Eastern country.

There were also widespread reports that North Korea helped Syria build a nuclear plant that was destroyed by Israeli bombing in 2007.

The West has ramped up its rhetoric following accounts of a deadly chemical attack outside Damascus on August 21, which it blames on Assad's regime.

Washington has accused Syria of trying to destroy evidence from the attack last week, which opposition forces say killed 1,300 people, including children.

Independent medical agency Doctors Without Borders has said at least 355 people died from "neurotoxic symptoms."

On Monday a team of UN inspectors sent to Damascus to investigate the claims came under sniper fire.

U.S. Secretary of State John Kerry said the use of chemical weapons was "undeniable" and warned that Syria would face a response for its actions.

"Let me be clear. The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity," Kerry said.

The right-of-center Sankei Shimbun is one of Japan's five nationwide newspapers and has a track record of publishing exclusive articles on North Korea. While the tone is often strident, it is generally thought of as a credible source on the subject.