N`Djamena: Long tailbacks form at a bridge on the border between Chad and Cameroon while Chadian security forces, wary of deadly Boko Haram jihadists, screen all road users and their property.
"We`re looking for weapons," a police officer explains at the Ngueuli bridge on the main road for imports to landlocked Chad, linking the capital N`Djamena to the far north of Cameroon.
Customs officials and security forces search men, women and children alike for arms being smuggled to the Nigeria-based Islamic extremists who have spread terror throughout the region. They also watch out for incoming explosives.
"There are no exceptions," a policeman says as he fleeces the pockets of a 13-year-old boy. "Have you seen how Boko Haram sends little kamikaze girls to blow themselves up in the middle of crowds? We don`t want that happening here."
Every day thousands of traders and travellers cross the bridge, which opens at 7:00 am (0600 GMT) and closes at nightfall. They include children from the Cameroonian border town of Kousseri who go to school in N`Djamena.
Chad, whose battle-hardened troops are leading a four-nation regional offensive against the Nigerian insurgents, is seeking to prevent Boko Haram attacks on its soil, like in Cameroon and Niger.
Chadian soldiers have played a decisive part in weakening the sect since they deployed in Nigeria in February, as part of the operation conducted alongside the armies of Cameroon, Niger and Nigeria itself.
N`Djamena lies only about 50 kilometres (30 miles) from Nigeria`s northeastern Borno state, the stronghold of the radical Islamist movement.
"We`ve launched open warfare against these people, we can`t deny that there`s a threat: bombs in the mosques and in the markets, that`s their specialty," says Abakar Walar Modou, general secretary of the King Faisal University in N`Djamena, who knows the Islamist sect well.
Patrols by police and paramilitary gendarmes have been increased considerably on N`Djamena streets of late. Hundreds of people have been arrested after identity checks, which have become systematic in districts with a sizeable Nigerian community.
Security sources in N`Djamena say that Boko Haram fighters regularly enter Chad to seek refuge or to buy weapons.
A few weeks ago, 19 suspected members of the sect were detained as they crossed the border from Cameroon in the Bongor region, some 200 miles south of N`Djamena, according to a police captain who asked not to be named.In a bid to stem such infiltration, Chadian authorities have halted all navigation on the Chari river and its tributary, the Logone, which both flow along the border between Chad and Cameroon.
Beneath the Ngueli bridge, the river once crossed daily by countless dugout boats in either direction now flows still and empty.
However, the stringent regulations are hurting the Chadian economy, which relies for maritime trade on the Cameroonian port of Douala on the Atlantic coast.
N`Djamena residents are paying the price.
"Crossing the bridge is a huge bother," says Ahmad, a trader. "Now when you return with only a small bag, they carry out a 100 percent search. You need ID and everything."
Many manufactured items, from farming tools and spare parts for motor vehicles to portable phones, are imported to Chad, a deeply poor and partly arid country that began to exploit its oil reserves a dozen years ago.
The bulk of the imported produce is transported by heavy goods vehicles to Kousseri, along a road that follows the border between Cameroon and Nigeria. On many occasions, the trucks have been attacked.
Supplies by road are increasingly scarce as a result, leading to a sharp rise in prices. "Many things have become too expensive," says Awa, a shop worker of about 40. "Even hot peppers cost too much."
Awa makes do by buying beer in Kousseri and bringing it home for sale. "They say that Boko Haram has made this trip difficult. We are living like this, but it is tough."