Suspected opposition activists attacked a passenger bus defying an opposition-called transport blockade with gasoline bombs, injuring 13 people on board, police said Friday.

The attackers hurled the gasoline bombs at the bus, which was part of a convoy being escorted by police after midnight near Basamadi village on the Mahendra highway in southern Nepal. The area is about 160 kilometers (100 miles) southwest of the capital, Katmandu.

Police official Birendra Khadka said after the bus was hit, the driver lost control of the vehicle and it flipped on its side. The passengers managed to escape by breaking the rear windows. There were 40 people on board the bus at the time of the attack.

The attackers fled in the darkness. Police believe they were supporters of the alliance of 33 opposition parties who have been attacking vehicles to enforce their nine-day transport blockage since Tuesday aimed at disrupting next week's elections in Nepal.

A similar attack on a passenger van on Wednesday in Katmandu left nine people injured.

The opposition alliance is demanding a stop to next week's elections and a change in government. They ordered the nine-day transport strike after enforcing a general strike on Monday that brought much of the country to a standstill.

The Nov. 19 polls to elect a Constituent Assembly are the second national elections since Nepal's 10-year civil war ended in 2006. A previous assembly was tasked with writing a constitution in 2008, following the overthrow of the centuries-old monarchy. But the assembly was riven by political battles and never accomplished its task.

The current interim government was formed by the major political parties and is led by the Supreme Court's chief judge. The opposition alliance is demanding the current government be disbanded and a new government with representation from all the political parties be formed to conduct elections at a later date.