DUBAI: Three Iranian military personnel were killed in south-east Iran early on Wednesday when the vehicle they were travelling in was struck by a roadside bomb, Iranian media said.

The reported killings, near to where the borders of Iran, Pakistan and Afghanistan meet, come at a time of heightened tension in the region as separatist Sunni Islamist militants step up attacks on officially Shia Iran.

Heavily-armed drug smugglers are also active in the region.

The three men were part of an engineering division of the Islamic Revolutionary Guard Corps (IRGC) working on construction projects near the city of Saravan, Tasnim news agency quoted an unnamed provincial official as saying.

In early November gunmen shot dead a public prosecutor and his driver in the city of Zabol, also in the border area, in reprisal for the hanging of 16 prisoners who were accused of being terrorists.

Days before that, militants killed 14 Iranian border guards in an attack near Iran's frontier with Pakistan. The previously little known group Jaish ul-Adl said it had carried out the attack.

Following Iran's 2010 execution of the leader of the Balochi separatist Sunni group Jundollah, analysts say there has been a radicalisation of armed insurgents in the Sunni majority region, with militants advocating a noticeably more al Qaeda-style international 'jihad' or holy war.

Rights groups have documented more than 400 executions in Iran so far in 2013.

At least 125 of those have been carried out since the election of President Hassan Rouhani on June 14, Human Rights Watch said recently.