Turkey has detained four suspected members of the Islamic State extremist group in the southeastern city of Gaziantep accused of planning a major attack, the Dogan news agency said Thursday.

Police seized 150 kilograms (330 pounds) of explosives, detonation equipment and two Kalashnikovs, the report said, with Turkey on high alert after the New Year Istanbul nightclub attack claimed by IS.

Dogan said IS leaders in northern Syria had ordered members to carry out a "sensational" attack in Turkey.

As well as the explosives and Kalashnikovs, police seized equipment for making suicide bombs, devices for setting bombs off via mobile phone, a pistol and cartridges.

Dogan said the stash had been buried under the earth in an open area and was found by sniffer dogs after the suspects were questioned.

A video showed sniffer dogs locating the cache and then the explosives and Kalashnikovs being uncovered.

The operation came just over a month after 39 people, mainly foreigners, were killed on New Year's Eve when a gunman went on the rampage inside a plush Istanbul nightclub.

IS claimed the massacre, its first clear claim for a major attack in Turkey, although it was blamed for several bombings in 2016.

Last weekend security forces detained over 750 people suspected of IS links in Turkey's biggest ever crackdown against the group.

Turkey was long accused by its Western allies of not doing enough to stop the flow of jihadists across its borders and emergence of IS cells in its own cities, including Gaziantep.

Ankara denies the charges, saying it has listed IS as a terror group since 2013. However, observers say Turkey has markedly stepped up its actions against the group in the last few months.

Police captured alive the suspected Reina nightclub attacker, Abdulgadir Masharipov, an Uzbek national, on January 16 after more than two weeks on the run and observers believe he may provide crucial intelligence.