Story highlights Experts say drill, called Yildirim, or "lightning bolt," is a warning from Turkey to Syria

Relations between nations had warmed in past decade; pair once had joint border maneuvers

But Turkey has watched Syrian government's crackdown on civilians with growing concern

As relations continue to deteriorate between neighbors Turkey and Syria, the Turkish armed forces announced Tuesday it will conduct a weeklong series of military exercises in a province along the Syrian border.

The objectives of the Yildirim ("lightning bolt") exercise include establishing coordination between military and civilian institutions and "testing of mutual activities performed during mobilization and war times," according to a statement on the Turkish Armed Forces website.

Some Middle East experts immediately interpreted the announcement as a warning to Damascus.

"Turkey is sending a signal to Syria," said Lale Kemal, a defense expert and Ankara bureau chief with the Turkish newspaper Taraf.

"The irony is that it was only a few years ago as part of improved relations that Turkey and Syria started joint border maneuvers."

Over the last decade, once frosty ties between Ankara and Damascus dramatically improved. The two countries signed a free trade agreement, held joint Cabinet meetings and removed visa requirements from each others' citizens.

But Turkey has watched the Syrian government's bloody crackdown on the country's six-month-old protest movement with growing concern.

More than 10,000 Syrian refugees have fled across the border to camps in Turkey in recent months, while hundreds of Syrian demonstrators suffering from gunshot wounds have been treated at Turkish hospitals.

On Tuesday, Turkey's prime minister stepped up criticism of Syrian President Bashar al-Assad, his former ally. During a state visit to South Africa, Recep Tayyip Erdogan endorsed a proposed United Nations Security Council resolution that would demand Syrian security forces immediately suspend their crackdown against anti-government protesters.

"We cannot remain a mere spectator to the developments in Syria," Erdogan told television cameras. "There are serious deaths against unjustly treated, oppressed and defenseless people. We cannot say 'keep going' to this ... we have to fulfill our human task."

Erdogan also said he planned to visit Syrian refugees living in camps along the Turkish border. That expected visit is likely to coincide with the Turkish military exercises near the border.

This week, a Turkish official told CNN on condition of anonymity that Turkey was considering taking "a series of steps" against the Syrian government. For weeks, the Turkish media has speculated about the possibility of Ankara establishing military buffer zones along the border, economic sanctions and the freezing of Syrian government assets.

Meanwhile, on Sunday, Turkey hosted a group of opposition activists in Istanbul. They announced the formation of a Syrian National Council seeking to challenge the authority of the Syrian regime.

Just a few years ago, Erdogan and al-Assad smiled side by side with their wives while attending a ribbon-cutting ceremony at a Turkish shopping mall.

Now, the Turkish leader has indicated that friendship may be over.

"We have to continue our friendship based on principles," Erdogan said in South Africa, according to the semiofficial Anatolian news agency. "If these principles are broken, if they are left aside, then we also leave that friend aside."