KANO (Nigeria): An explosion near a bus station in the northeast Nigerian city of Gombe killed at least five and injured 15 others, in an attack that bore the hallmarks of Boko Haram.

"We had an explosion outside the motor park (bus station) this evening around 8.30pm local time (0100 IST Friday) which killed five people and injured 15 others," said Muhammad Garkuwa, a drivers' union official.

"The explosion was from an explosive left by a woman in her handbag beside a bus waiting to convey passengers to Jos," he said in an account supported by a nearby food seller.

The attack on Thursday is the latest in a string of similar explosions against so-called "soft targets" such as busy bus stations and crowded markets in the restive northeast, which has been hit for the last six years by Boko Haram Islamists.

The group has been pushed out of captured territory in Yobe, Borno and Adamawa states since February by a four-nation coalition of troops from Nigeria, Niger, Chad and Cameroon.

Since then, the group has reverted to guerrilla tactics, including suicide bombings and attacks on civilians in urban centres.

Garkuwa said he loaded the casualties into a vehicle while Yusuf Darazo, who sells food near the bus station, said the female suspect left her bag after being told the bus's destination.

"No-one suspected her. People around assumed she was making calls before the bus filled up," he said.

"As she was talking in the phone she moved away from the bus towards a row of kiosks, as if she wanted to buy something, leaving her bag where she was standing.

"She disappeared and the bag exploded soon after, setting the bus on fire. I saw five dead and several injured."UNITED NATIONS: Some 519 people have been killed and nearly 1,700 injured in two weeks of fighting in Yemen, the UN aid chief has said, raising alarm over the fate of civilians.

Valerie Amos yesterday said she was "extremely concerned" for the safety of civilians trapped in the fierce fighting and appealed to armed factions to do their utmost to protect ordinary Yemenis.

The violence has sharply escalated in Yemen following a Saudi-led air campaign launched on March 26 to stop an advance by Shia Huthi rebels that forced President Abedrabbo Mansour Hadi to flee to Saudi Arabia.

Aid groups have expressed alarm over the mounting toll of civilian casualties following an air strike on a camp for displaced people and the bombing of a dairy. Dozens were killed in both attacks.

"Those engaged in fighting must ensure that hospitals, schools, camps for refugees and those internally displaced and civilian infrastructure, especially in populated areas, are not targeted or used for military purposes," Amos said in a statement.

The UN children's agency this week said at least 62 children had been killed and 30 injured over the past week in Yemen, and that more of them were being recruited as child soldiers.

Tens of thousands of people have fled their homes, some making the perilous journey by sea to Djibouti and Somalia, Amos said.

UN aid agencies are working with the Yemen Red Crescent to deliver emergency health kits and generators so that civilians can have clean water, food and blankets, she added.

UN secretary-general Ban Ki-moon this week reminded all sides to uphold international humanitarian law and protect civilians.

The United Nations is backing Hadi as Yemen's legitimate leader in the face of the Huthi uprising that has plunged the poor Arab state deeper into chaos.

The Huthis seized power in the capital Sanaa in February and last month advanced on the port city of Aden, Hadi's stronghold, where they seized the presidential palace on Thursday.