Attackers have killed two border guards and injured another near Saudi Arabia's border with Iraq in a shooting and suicide assault, according to the kingdom's Interior Ministry.
The attackers opened fire on a border patrol near the city of Arar early on Monday, the ministry said.
When security officers responded, one of the attackers was captured and detonated an explosives belt, the ministry said in a brief statement carried by the official Saudi Press Agency.
It said another attacker was killed by security forces but did not specify the number of assailants.
Al Jazeera's Imran Khan, who has been covering the conflict in Iraq, says the attack was probably carried out by fighters of the Islamic State of Iraq and the Levant (ISIL) group, which controls large parts of Iraq and Syria.
"ISIL has attacked the border before," he said.
"ISIL has long held that the Saudi royal family doesn't have legitimacy and therefore is a target.
"This attack is only likely to strengthen the resolve of Riyadh and Baghdad to strengthen relations, which includes reopening the Saudi embassy in Baghdad which has been shut for nearly 25 years, and to fight ISIL."
But Saudi's Interior Ministry said that it would not know which group was responsible until it had identified the remains of the attackers, a process it said would take some time.
Saudi Arabia has joined the US-led alliance against ISIL and is participating - along with Jordan, Bahrain and the United Arab Emirates - in air strikes in Syria, with logistical support from Qatar.
The move has drawn threats of retaliation from the group.
In a purported audio recording released on social media networks last month, ISIL leader Abu Bakr al-Baghdadi warned Saudi leaders they would see "no more security or rest."
In July, three shells fired from inside Iraq hit the Arar area, without causing any casualties. No group claimed responsibility for that attack.
On Saturday, Saudi media announced that a Saudi delegation would travel to the Iraqi capital in the coming week to start preparations to reopen an embassy.
Saudi Arabia closed its Baghdad embassy in 1990 after the late Iraqi leader Saddam Hussein invaded Kuwait
Since the overthrow of Saddam in 2003 after a US-led invasion and the installation of a Shia-dominated government in Baghdad, Saudi Arabia has accused Iraq of being too close to Shia Iran, its main regional rival.
It has also accused Iraqi governments of encouraging discrimination against Sunnis.
Iraq has consistenly rejected those accusations.
Source: Al Jazeera and agencies