By Nnekule Ikemfuna

KANO, Nigeria (Reuters) -- Two female suicide bombers blew themselves up at a mobile phone market in the northern Nigerian city of Kano on Wednesday, killing at least 14 people and wounding more than 100 others, the country's emergency response agency said.

The explosions occurred around 4 p.m. local time (1500 GMT) at the Farm Center phone market, near the center of Nigeria's second biggest city, and come a day after a blast in the northeastern city of Yola killed 32 people and wounded 80 others.

The attacks bear the hallmarks of Boko Haram, suggesting that the militant Islamist group, which has killed thousands over the last six years in its bid to create a state adhering to strict Sharia or Islamic law in the northeast, is stepping up its operations.

"Over 100 persons injured and 14 others lost their lives in today’s market bomb blast in Kano," said Sani Datti, a spokesman for the National Emergency Management Agency (NEMA).

Suspected members of Boko Haram have killed more than 1,000 people since President Muhammadu Buhari took office in May.

"President Buhari reassures Nigerians that his administration is very much determined to wipe out Boko Haram in Nigeria and bring all perpetrators of this heinous crime against humanity to justice," said presidency spokesman Garba Shehu.

He said Buhari urged vigilance to help ward off suicide terror attacks on "soft targets", adding that Nigeria's "reinvigorated, well-equipped and well-motivated armed forces and security agencies" would overcome Boko Haram very soon.

Since losing most of the territory they took over earlier this year to the Nigerian army, the militant group has focused attacks on markets, bus stations and places of worship, as well as hit-and-run attacks on villages.

Suspected Boko Haram militants have carried out attacks in neighboring Chad, Niger and Cameroon in recent weeks but until Tuesday had not struck northeastern Nigeria since late October.

In Washington, the State Department condemned "horrific" bombings in the northern towns of Yola and Kano in recent days, and said the United States was committed to working with Nigeria and its neighbors to defeat Boko Haram.

"We denounce the callous terrorist acts," spokesman John Kirby said, adding: "Those responsible for these crimes must be held accountable."

(Additional reporting by Isaac Abrak and Camillus Eboh, and Lesley Wroughton in Washington, writing by Alexis Akwagyiram; editing by Richard Balmforth)