Ammunitions were recovered from the premises of a girls' school in Gampola, the police said on Sunday.
A labourer of the school had recovered the parcel, consisting of 201 rounds of T56 ammunition and 25 pistols, at a garbage dump during the cleaning of the school, Daily Mirror reported.
The labourer had then informed the security unit of the school, who later informed the police and the Army.
The police suspected that due to intensified raids in the area in the wake of the Easter Sunday attacks someone must have thrown away the ammunition parcel into the school premises.
Earlier, the police had also arrested two wanted suspects, identified as Mohamed Iwuhaim Saadiq Abdul Haq and Mohamed Iwuhaim Shahid Abdul Haq, in Gampola over the Easter Sunday attacks.
Meanwhile, Sri Lanka has expelled around 200 Islamic clerics after a local terror group, National Thowheed Jammath, claimed responsibility for the Easter bombings that left at least 253 people dead and several hundred injured, state media reported.
The clerics are believed to have entered the country legally, but due to security crackdown after the attacks, they were found to have overstayed their visas for which fines were imposed and they were expelled from the island.
Without providing any further details on the people who were expelled, the government claimed that many foreigners who have overstayed their visas since the Easter attacks were from Bangladesh, India, Maldives and Pakistan.
On April 21, eight explosions rattled Sri Lankan cities of Colombo, Negombo, Kochchikede and Batticaloa as the Christian community celebrated Easter Sunday.