COLOMBO, Sri Lanka (CNN) -- At least 26 people were killed and more than 50 were wounded Wednesday in a pair of attacks in southern Sri Lanka, authorities said.
The government has stepped up patrols in Colombo since the end of the ceasefire.
The attacks prompted the government to close schools in the area. Police believe the attacks were engineered by Tamil Tiger rebels.
The first attack targeted a bus carrying factory workers, killing 10 men and 13 women, police and military sources said. More than 50 people were injured.
Initially, authorities thought the attack targeted a school bus, which prompted the school closings.
A senior police official in Colombo told CNN a Claymore mine detonated near the bus. "Thereafter, the rebels opened fire and hurled grenades at the bus," the official said.
Communications were spotty, and authorities were having a tough time reaching the town, about 238 miles (383 km) east of Colombo and near the southern town of Buttala.
In the second attack, also near Buttala, another Claymore mine targeted an armored military vehicle. That blast wounded three soldiers, military sources said.
Violence has increased in the island nation since the government gave a required two weeks notice of its intentions to withdraw from a 2002 cease-fire. The blasts on Wednesday came at the end of that two week period - on the day the Sri Lankan government formally withdrew from the agreement.
Major international aid donors expressed concerns about that decision. In a joint statement, Norway, Japan, the United States and the European Union told Colombo on Saturday that there is no military solution to its escalating conflict and urged it to seek "a negotiated settlement" with the rebels.
The Tamil Tigers have declared they would abide by the cease-fire and called on Norway to continue its role as peace facilitator.
Explosions have occurred in the high-security zone of the capital, including at the Defense Ministry and the army, navy and air force headquarters. Last week, D.M. Dassanayake, a non-cabinet minister for nation-building, died after a roadside bomb struck his convoy, police said.
The violence has prompted at least one foreign government to revise its travel advisory regarding Sri Lanka. German travel operators, who typically send a large volume of tourists to the country, have suspended their operations.
Even before the Sri Lankan government's announcement, the cease-fire -- brokered by Norway in 2002 -- existed in name only. The two sides resumed fighting two years ago.
The government and rebels have engaged in a brutal civil war since 1983. The rebels, formally called the Liberation Tigers of Tamil Eelam, want an independent homeland for the Tamil minority in the north and east of the island nation, located south of India. They cite decades of discrimination by the majority Sinhalese.
About 65,000 people died before the two sides reached the 2002 truce. E-mail to a friend