Two Iranian border guards and a Pakistani paramilitary officer were killed in a shooting incident, sources on the two sides said Friday, as Tehran said rebels tried to infiltrate the country.
"Several rebels" also died in the fighting Thursday night, Iran's news agency ISNA quoted a military official as saying, adding that a car and weapons were seized.
Meanwhile, an official in Pakistan said a paramilitary officer was killed and four soldiers wounded when their vehicle came under fire by Iranian border guards.
"The FC (Frontier Corps) patrol was chasing two suspects in a car when the Iranian border guards opened fire from across the border, killing one junior commissioned officer and wounding four soldiers," spokesman Wasey Khan told AFP.
The home secretary of Pakistan's Baluchistan province, Akbar Hussain Durrani, confirmed the incident and the casualties.
It was not clear if the car being pursued by the Pakistanis was the same one seized after the shooting incident across the border.
Baluchistan is adjacent to the Iranian province of Sistan-Baluchistan, where ISNA said the shooting occurred and where rebel attacks earlier this month killed five people, four of them security forces.
Iranian media said 14 people were arrested in connection with those attacks.
Last month an Iranian soldier was killed and two pro-government militiamen wounded in an attack blamed on the Sunni extremist group Jaish-ul Adl (Army of Justice).
The same group captured five Iranian soldiers in February, four of whom were released in April. The fate of the fifth man remains unknown.
Sistan-Baluchistan province has a large Sunni Muslim community in an otherwise predominantly Shiite country, and has been plagued by violence involving Sunni extremists and drug smugglers.
Iran has repeatedly asked Pakistan to act to "stop the infiltration of terrorists" and has tasked the elite Revolutionary Guards to monitor the restive border region.
Pakistan's resource-rich Baluchistan is home to a long-running separatist conflict that was revived in 2004, with nationalists seeking to stop what they see as the exploitation of the region's natural resources and alleged rights abuses.
The idea of giving greater autonomy to the province, the size of Italy but with only nine million inhabitants, is highly sensitive in a country still scarred by the independence in 1971 of its eastern portion, now Bangladesh.