There have been a number of rounds of border skirmishes between Iran and Pakistan since the first week of October. However, reports that Pakistani forces have returned mortar fire is highly unusual and represents an increase in tensions that have marred this region for years. Last week some 30 Iranian security force personnel crossed the border in pursuit of anti-Iranian militants. The Iranian raid resulted in the death of a Pakistani Frontier Corps soldier. Islamabad lodged a diplomatic protest. A meeting on Wednesday in Tehran on increasing intelligence sharing between the two countries was meant to end this latest spat. That meeting clearly did not achieve its objective. The problem is considerably deeper than merely finding ways to share intelligence about border crossings. Officials in Tehran have for years maintained that the Pakistani side is either incapable or reluctant to stop cross-border attacks. In fact, Iranian officials often accuse elements in Pakistan - with the alleged backing from Gulf States - of providing sanctuary and support to anti-Iranian militants to try to create instability for Tehran. The Pakistanis have always rejected such charges. Turning point The militants at the heart of the dispute are from Jaish Al-Adl (Army of Justice). It is an ethnic Baloch and Sunni group which purports to fight for better living conditions in Sistan Baluchistan, Iran's most impoverished province. It is widely believed to be the successor to Jundullah, another Iranian Baloch group, which the United States in 2010 designated a terrorist organisation. Jundullah, which emerged on the scene around 2003, was responsible for the deadliest attacks against Iranian government targets, including an assassination attempt against then President Mahmoud Ahmadinejad. The group's most high-profile attack took place on 18 October 2009 in the border town of Pishin. A suicide bomber that Tehran claimed had crossed the border from Pakistan blew himself up at an assembly of Iranian Baloch tribal leaders and senior commanders from Iran's elite Revolutionary Guards (IRGC). Among the dead was Noor Ali Shooshtari, the deputy commander of Ground Forces of the IRGC, a man close to Iran's Supreme Leader Ayatollah Ali Khamenei. That attack was a turning point. Major difference It is most likely not a coincidence that the recent attacks by Jaish Al-Adl come on the fifth anniversary of the Pishin attack. As is the case today, top commanders from the Revolutionary Guards then vowed to retaliate and put extreme pressure on Pakistan. It was most likely with Pakistan's help that, within four months of the Pishin attack, Iran was able to capture Abdolmalek Rigi, the young leader of Jundullah. Rigi was hanged in Tehran in June 2010. The most recent Iranian actions, including the pursuit of militants across the border and shelling inside Pakistani territory, is very similar to what occurred in the aftermath of the Pishin attack. The major difference this time, however, is that the Pakistani side is now openly returning fire against Iran. This amounts to an escalation that breaks with past Pakistani behaviour. Islamabad, which over the last few weeks has also had to deal with skirmishes on its Afghan and Indian borders, apparently feels it has to react to deter the Iranians from any further unilateral action. The record from the last decade shows that both sides are disinclined to let the violence get out of control. Tehran and Islamabad have for a long time been willing to accept "contained hostilities" in the border regions as part of life and assumed that border violence will always be limited and localised. That is a dangerous and potentially a very costly assumption. Alex Vatanka is the author of a forthcoming book on Iran and Pakistan: Security, Diplomacy and American Influence, to be published by IB Tauris. BBC News - Iran-Pakistan: Will border tensions boil over?