Greek Prime Minister Alexis Tsipras speaks during a parliament session in Athens on March 10, 2015. (Petros Giannakouris/AP)

The complexity of international diplomacy rarely spills over into the 140-character world of Twitter. On Sunday, however, observers were astonished when Greek Prime Minister Alexis Tsipras took to the platform to harshly criticize Turkey -- only to delete the comments shortly afterward.

"Fortunately our pilots are not as mercurial as yours against the Russians," Tsipras wrote, referring to the recent downing of a Russian military plane by Turkey after it allegedly crossed into the country's airspace. "What is happening in the Aegean is outrageous and unbelievable ... We're spending billions on weapons. You -- to violate our airspace, we -- to intercept you," Tsipras continued in multiple Tweets. Hundreds of refugees trying to reach the Europe Union have drowned in the Aegean Sea, which is located between Greece and Turkey.

Tsipras accused Turkey of being unwilling to save the lives of refugees. "We have the most modern aerial weapons systems -- and yet, on the ground, we can't catch traffickers who drown innocent people," he wrote, before deleting the four tweets on his English account. On Tsipras' Greek account, the tweets remained published as of Monday morning.

The comments, which were addressed to Turkish Prime Minister Ahmet Davutoğlu, were made on the sidelines of  an E.U.-Turkey refugee summit in Brussels that both leaders attended. Turkey is expected to receive $3.2 billion from the E.U. to help refugees in the country and to clampdown on the flow into Europe.

Tensions between Turkey and Greece are longstanding. In 1974, the island of Cyprus in the Mediterranean was effectively partitioned, with the north later proclaiming itself the "Turkish Republic of Northern Cyprus." The Greek south does not recognize the Turkish north's independence. Greece and Turkey have so far failed to agree on plans to reunite the island's inhabitants, and tensions have periodically spike, or calmed down.

Replying to Tsipras' comments on Sunday, Davutoğlu urged his Greek counterpart to "focus on our positive agenda."

About an hour later, Tsipras appeared to backtrack from his previous comments -- but nevertheless emphasized the need to "talk honestly" with one another.