RIYADH (AFP) - A Saudi gunman was killed and another detained during a security forces operation in the north-east of the country that also left a policeman dead, the interior ministry said Saturday.

The two suspected militants were wanted for the murder of a soldier, two civilians and a policeman this week in the kingdom, state news agency SPA quoted a ministry spokesman as saying.

The operation was launched in response to a video shared on social media in which one of the two men appeared to shoot dead a man he had tied up, "at the request of the Islamic State group", he said.

The man was a soldier killed on Thursday by two of his cousins aged 18 and 20 near Al-Shamli, in Hail province, he added.

Investigators alleged the two brothers - Islamic State in Iraq and Syria (ISIS) followers - had also killed two civilians and a policeman in Al-Shamli on the same day, the spokesman said.

The gunmen, who were hiding in a mountainous region near Al-Shamli, refused to surrender and opened fire on security forces who retaliated, killing one and wounding the other, who was detained.

A policeman was caught in the crossfire and died.

Saudi Arabia is part of a US-led military coalition fighting ISIS in Iraq and Syria.

In recent months, Saudi authorities have increased arrests of alleged Sunni extremists suspected of having planned attacks to foment tension between different religious confessions in the country.

On July 18, the interior ministry announced it had disrupted a network linked to ISIS and made more than 430 arrests, foiling new attacks on Shi'ite mosques and a diplomatic mission.

Since May, ISIS has claimed four suicide attacks in Saudi Arabia.