KUALA LUMPUR – Malaysian troops and police were Wednesday hunting militant followers of a Philippine self-proclaimed sultan, who landed in Sabah state on Borneo to assert his historical claim to the area.

Following are key details on Sabah and the turmoil:

What is Sabah?

Sabah is a resource-rich Malaysian state about the size of Ireland on the north of Borneo island.

It has huge oil palm plantations, but also some of the world's best scuba diving and rainforest-clad mountain ridges that have earned it the nickname of Malaysia's "Wild East".

Along with Sarawak, it is one of two Malaysian states on Borneo, which is also shared by the tiny sultanate of Brunei and Indonesia's Kalimantan. The capital is Kota Kinabalu.

Who lives in Sabah?

While mainland Malaysia is dominated by Muslim ethnic Malays, Sabah's population has traditionally been overwhelmingly made up of Borneo tribes, many of whom are now Christian.

The federal government has faced accusations for more than three decades that it illegally gave hundreds of thousands of Muslim foreigners citizenship in return for votes for the ruling coalition.

The government has denied the charge.

But Sabah's population has surged from some 600,000 in 1970 to more than three million now and there are rising tensions between native Sabahans and foreign migrants.

The foreigners -- mainly poor economic migrants from the neighboring southern Philippines and Indonesia -- are blamed by locals for crime, drug abuse and competition for jobs.

Sabah's government said recently 28 percent of the state's people are of foreign origin.

What caused the current crisis?

The Sulu sultanate once controlled the Sulu islands in the Muslim southern Philippines and part of Borneo including Sabah, but the advance of European colonialism eroded its power.

It officially lost Sabah in 1878, via a loosely worded contract, to a British trading company. Sabah became a British colony and joined the new nation of Malaysia in 1963.

While Sabah has prospered, the remote Sulu islands are among the poorest parts of the Philippines and a breeding ground for insurgents who dream of a Muslim homeland independent from the government in Manila.

Descendants of the Sulu sultans have continued to receive nominal rent from Malaysia of about $1,700 per year for Sabah under a deal inherited from European powers.

The intruders' exact demands remain unclear but they have expressed resentment with the ongoing state of affairs.

Have similar incursions happened before?

Sabah has seen previous smaller-scale raids by Islamic militants and other bandits from the adjacent southern Philippines, which has suffered for decades from a Muslim insurgency.

A Philippine Islamic militant group seized 21 mostly Western holidaymakers from a scuba diving resort at Sipadan off Sabah, taking them to the Philippine islands.

They were later ransomed.

Two Malaysians were kidnapped from a plantation in the area in November and are believed to have been taken to the southern Philippines.

What is at stake?

The incident risks stoking tensions between Sabahans and Filipinos.

Meanwhile, the exposure of lax security could erode support for Malaysia's ruling coalition in Sabah, a battleground state in what are expected to be tightly fought national elections due by June.

The Philippines is also watching closely for any impact on a framework agreement reached in October with the main Muslim separatist group in its south to end a decades-long insurgency that killed more than 150,000 people.

The security crisis could also adversely affect tourism in Sabah.

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