[via]

Egypt may sue Turkey for alleged support of Muslim Brotherhood-linked terrorism.
The judicial source said Mahmoud had claimed in his case that Turkish President Recep Tayyip Erdo─čan had supported the Muslim Brotherhood movement and criticized Egypt following the ouster by the army of Islamist President Mohamed Morsi in July 2013.

The brotherhood, the movement from which Morsi hails, was declared a terrorist organization by the Egyptian government in December 2013 
Obviously, the Egyptian military has a vested interest in wiping out all traces of the Muslim Brotherhood. But these are some serious accusations:
The judicial source added that the lawyer filing the case also claimed that Turkey was the main source of arms entering Egypt that ended up in the hands of terrorists.
“Turkey [has adopted] hostile stances against Egypt after it became a haven for Muslim Brotherhood leaders who face criminal charges in Egypt,” the judicial source quoted Mahmoud as saying in his lawsuit.
Meanwhile, another majority Arabic Muslim state has accused Turkey of supporting terrorism.
“They (Turkish authorities) say that the border is too broad and they cannot control it. I believe that they can control it. It is in the interest of our partners to stop the flow of terrorists to Iraq,” Prime Minister Haider al-Abadi said at the 51st Munich Security Conference in Germany on Saturday.

Turkey has come under international criticism for allowing thousands of foreign terrorists to join Takfiri groups such as ISIL, which has captured some parts of Iraq and Syria.

Interpol has warned that foreign terrorists are increasingly going to Turkey through booking tickets on cruise ships to join Takfiri groups in Syria and Iraq.
In Turkey's partial defense, porous border control is easier said than done.

After all, the U.S. can hardly contain the flow of cartel-distributed drugs from across the Mexican border that fuels violence in major cities like Chicago.
The drug trade in Chicago has helped fuel pervasive gang violence that has resulted in a quickly rising homicide rate. Chicago ended 2014 with 425 murders, and this year the city had seen 30 slayings by the end of January.
Then again, countries like Saudi Arabia and Qatar have explicitly funded various groups in Syria and Iraq, using Turkey as a base of operations.
Ankara has been quite public with its denunciation of Assad even as it denies any involvement in shuffling weapons across the border to Syrian rebels. It claims its territory is not being used to do so. And yet, as TIME reported in June, a secretive group operates something like a command center in Istanbul, directing the distribution of vital military supplies believed to be provided by Saudi Arabia and Qatar and transported with the help of Turkish intelligence to the Syrian border and then to the rebels. Further reporting has revealed more details of the operation, the politics and favoritism that undermine the task of creating a unified rebel force out of the wide array of groups trying to topple the Assad regime.
Currently, Erdogan seems more concerned with rooting out all (real or imagined) signs of a Fethullah Gulen insurrection (whose own Chicago ties I've written about here) than the perception that the country is clashing with its previous allies and becoming a hub of the region's problems:
That is why I think Turkey is increasingly becoming an important part of the problems and coming close to becoming the center of crises in the Middle East – not because Turkey under the AKP is challenging the Western powers, as its supporters claim. Instead, it is because Turkey’s rulers have ultimately turned the country into a volatile and unpredictable political actor for both its friends and foes internationally and increasingly autocratic domestically.
Whatever course Erdogan takes his country in, it'll follow his vision of a powerful, influential, independent Turkey -- global ramifications and public opinion be damned.