NEW DELHI, India (AP) _ A minister from Tamil Nadu state resigned Monday, posing a challenge to P.V. Narasimha Rao's five-week-old government, which relies on the Tamil Nadu government for support.

Press Trust of India said Labor Minister Vazhapadi Rammurthy resigned to protest the government's decision to ask the Supreme Court to resolve a 25- year dispute between Tamil Nadu and the neighboring state of Karnataka over control of water from the Cauvery River.

Rao, who heads a minority government, does not want to displease the Tamil Nadu government because it is ruled by the All India Anna Dravida Munnetra Kazagham party, a key ally of Rao's Congress Party in Parliament.

Rammurthy's resignation was likely to drive a wedge between Parliament members from Tamil Nadu and those of Karnataka, which is governed by Congress. The two states are in southern India.

Rammurthy charged the government's decision was unfair because a Supreme Court-appointed tribunal had already demanded that Karnataka release additional water from a dam on the Cauvery, which flows from Karnataka to Tamil Nadu. Earlier this month, Karnataka refused to obey the tribunal's order.

Tamil Nadu, strapped for drinking water, claims that Karnataka uses more than its share of the river water.

''We need water and do not want clarification for any legal dispute,'' Rammurthy, 52, was quoted as saying by United News.

The Congress Party depends on Tamil Nadu for support in the Lok Sabha, the law-making, lower house of Parliament.

Congress Party won 225 seats in the May-June elections. The All India Anna Dravida Munnetra Kazagham has 11 seats, and nine other members of smaller parties support Congress. Although still short of majority in the 507-member house, Congress survives by tacit support from a centrist-leftist alliance.

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