Jordan expelled Syria's top envoy Monday, prompting Damascus to do the same in a diplomatic tussle that could signal the start of unraveling ties between the neighbors.
The move came a week before an election in Syria expected to keep President Bashar Assad in power. The highly contentious vote, being held amid a ferocious civil war, has been called a mockery by Western countries.
It was unclear what specifically caused Jordan to expel Syrian Ambassador Bahjat Suleiman. Jordan has hosted an envoy from Syria since the start of the 2011 uprising despite quietly supporting rebels trying to overthrow Assad.
Suleiman was ordered to leave the country within 24 hours in a humiliating public announcement first made on state-run media.
He was declared persona non grata because of "continued offensive statements, through his personal contacts or writing in the media and the social media, against the kingdom," Jordanian Foreign Ministry spokeswoman Sabah al-Rafie said in a statement carried by the state-run Petra news agency.
His statements were a "sheer departure from all diplomatic norms and conventions," she said.
Al-Rafie said Suleiman used Jordan as a platform to offend other Arab countries, likely referring to Saudi Arabia and Qatar, both chief supporters of the Syrian rebels.
Syrian officials and diplomats regularly launch diatribes against the leaders of those countries and Turkey.
Soon after the announcement from Amman about Suleiman, Syria's Foreign Ministry said it would expel the Jordanian charge d'affaires in retaliation, although he was not in the country. It said it requested the Jordanian Embassy in Damascus to inform the diplomat that he is banned from entering Syria.
"Jordan's reprehensible and unjustifiable decision does not reflect the deep fraternal relations between the two peoples in Syria and Jordan," it said.
Jordanian Information Minister Mohammad al-Momani said the ambassador to Syria retired a month ago and a replacement had not been assigned.
The main Western-backed opposition group, the Syrian National Coalition, welcomed Jordan's move, calling it an "important step" in supporting the Syrian people. In a statement, the coalition urged other Arab states to follow Jordan's lead to increase the Assad government's isolation.
Experts expressed surprise at the Jordanian announcement, saying it was not in keeping with diplomatic protocol.
"The dramatic way he was expelled was strange. It's as if Jordan is cutting off its diplomatic relations with Syria," said analyst Hisham Jaber, a retired brigadier general in the Lebanese military.
"The ambassador could have been summoned, and a complaint could have been lodged. But to say: `Get out' -- that's very tough."
A Facebook page created by Suleiman's supporters suggested his defiance and loyalty to Assad. The "Network of those who love Mr. Ambassador Dr. Bahjat Suleiman" posted what it said was his expulsion notice from Jordan. The page later contained a photo claiming to show Suleiman being carried on the shoulders of his backers. "Syria needs you more," was emblazoned across it.
Suleiman had headed one of Syria's most powerful internal intelligence branches and was sent to Jordan as ambassador in 2009, perhaps after a falling out with Assad's inner circle, Jaber and Syria analyst Aron Lund said.
It was unclear if the diplomatic tussle will have any long-lasting repercussions, including on the two countries' shared border.
Rebels control Syria's borders with Iraq and Turkey, leaving only the Lebanese and Jordanian border posts in the government's hands. The corridor with Jordan allows Syrian products to reach wealthy Gulf markets, helping an economy shattered by three years of civil war.
Jordan also hosts nearly 600,000 registered Syrian refugees -- although Jordanian officials say the number is far higher.
In an interview with The Associated Press, Syria's ambassador to Lebanon, Ali Abdel-Karim Ali, said the upcoming election will be the resounding answer to those who doubt Assad's government will prevail in the conflict. He said he expects a huge turnout for the vote, to be held abroad Wednesday and inside Syria on June 3.
He said Western leaders such as U.S. President Obama, British Prime Minister David Cameron and French President Francois Hollande criticize and oppose the election because they fear the results.
"The Syrian people will say their word in these elections, and their word is the one that counts. Not Obama's word, Cameron's or Hollande's," Ali said.
Assad is all but guaranteed victory because opposition groups are boycotting the vote, which will only be held in government-held areas of the fragmented country. Rebels control vast territory of Syria.
More than 160,000 people have been killed and millions displaced since the uprising began in March 2011 and became a civil war.