Faced with stiff resistance from the Tamil Tigers, Sri Lanka has ordered emergency military supplies from Pakistan, according to official sources in India.

In a development noted with some concern by the Indian establishment, the Sri Lanka Army has sought 150,000 rounds of 60 mm mortar ammunition and as many hand grenades for immediate delivery, the sources said.

Sri Lanka has also requested $25 million worth of 81 mm, 120 mm and 130 mm mortar ammunition to be delivered within a month, the sources told IANS.

General Sarath Fonseka, the Sri Lankan army chief who spent six days in India last month, has conveyed the requirements to his Pakistani counterpart, General Ashraf Pervez Kayan.

The Pakistani military has apparently agreed to supply the ammunition on an emergency basis from its War Wastage Reserve maintained in various army depots.

The SOS comes amid escalating fighting in Sri Lanka where the military is desperately trying to gain control of areas the Liberation Tigers of Tamil Eelam holds in the island's north.

The current fighting is concentrated mostly in the districts of Mannar, Vavuniya and Mullaitivu, which along with Kilinochchi are commonly referred to as the Vanni region, as well as in Jaffna.

In Mannar, the military has been trying for months to advance into LTTE territory. And with rains starting around two weeks ago, the military push could slow down further.

The Sri Lankan military controls most of Mannar, Vavuniya and Jaffna. The Tigers are in control of the whole of Mullaitivu and Kilinochchi districts.

Despite some gains, the military is finding the going tough in the north, in contrast to the eastern wing of the country that came under Colombo's control in 2007 after the Tigers withdrew their forces.

The resistance the LTTE is putting up is making Sri Lanka turn to Pakistan to make up ammunition it is exhausting, the Indian sources said.

Sri Lanka started buying arms and ammunition from Pakistan in a big way from 1999. The total purchases until December 2007 were worth $50 million while there has been a sudden jump in the quantity of merchandise ordered this year.

Pakistan's main military supplies to Sri Lanka include mortar ammunition, radio sets, hand grenades, naval ammunition and tanks.

The military links between Islamabad and Colombo worry New Delhi because this gives Pakistan access to Sri Lankan defence establishments and intelligence that analysts here fear hurts Indian security interests in the long run.

India mainly provides what it says are non-lethal military supplies to Sri Lanka. And while refusing it offensive weapons, New Delhi has publicly expressed displeasure over Sri Lanka's military purchases from Pakistan and China.

Sri Lankan officials argue that they are free to go to any country for weapons supplies since India refuses to provide lethal weapons. Colombo says that in any case it keeps New Delhi informed about their shopping list.

A section of the Indian establishment feels that with so much military hardware pouring into Sri Lanka, the war in the island is unlikely to end any time soon.