The war of words between Syria and Turkey escalated on Thursday, when Ankara said it had found military supplies on a passenger plane it intercepted en route between Moscow and Damascus.

AFP reported that the Syrian foreign ministry accused Turkish Prime Minister Recep Tayyip Erdogan of lying after he said the jet had been carrying “equipment and ammunition shipped to the Syrian defense ministry” from a Russian military supplier.

Syrian authorities challenged Erdogan to show the weapons he alleged had been seized from the plane, which was intercepted by Turkish fighters on Wednesday and forced to land for an inspection before being allowed to fly on.

“The Turkish prime minister continues to lie in order to justify his government’s hostile attitude towards Syria,” the Syrian foreign ministry said in a statement quoted by AFP.

“The plane did not carry ammunition or military equipment and Erdogan’s comments lack credibility and he must show the equipment and ammunition at least to his people,” the information ministry said.

In the plane incident, Ankara scrambled two jets on Wednesday to force the Syrian Air airliner to land after receiving intelligence its cargo did not comply with civil aviation rules, Turkish officials said.

The aircraft with 35 passengers on board was grounded for nine hours before it was finally allowed to resume its journey to Damascus.

Damascus denounced the interception as “hostile and reprehensible… another sign of the hostile policies of the Erdogan government, which harbors (rebels) and bombs Syrian territory.”

It demanded Turkey return the cargo seized at Ankara’s Esenboga Airport.

Russia, Syria’s ally and main arms supplier, also denounced Ankara.

“We are concerned that this emergency situation put at risk the lives and safety of passengers, who included 17 Russian citizens,” said Russia’s foreign ministry, according to AFP.

It denied the plane had been carrying weapons or military equipment.

The plane incident occurred in the wake of a week of tension between Turkey and Syria, which began last Wednesday when a Syrian mortar landed in Turkish territory, killing five civilians in Akcakale.

The Turkish army responded by attacking several targets in Syria. Turkey’s parliament on Thursday gave the government the green light to use military force against Syria if necessary.

The United Nations Security Council later condemned Syria over the mortar attack on Turkey.