The Iraqi prime minister has said he will not bow to international pressure on forming a national unity government to tackle the Sunni rebellion in the north, calling the idea a "coup" against the constitution.

Nouri al-Maliki's statement on Wednesday came a day after the US secretary of state, John Kerry, left Iraq after pushing for an agreement between Kurdish, Sunni and Shia leaders.

In his weekly televised address, Maliki said: "The call to form a national emergency government is a coup against the constitution and the political process.

"It is an attempt by those who are against the constitution to eliminate the young democratic process and steal the votes of the voters."

The speech came a day after US military advisers arrived in Baghdad. The US says Iraqi politicians must create a unity government before it sends futher help.

Al Jazeera's Imran Khan, reporting from Baghdad, said Maliki's comments would be seen as direct rebuttal to the US insistence of a unity deal before more help is sent.

Maliki's electoral bloc won by far the most seats in April 30 parliamentary elections with 92, nearly three times as many as the next biggest party, and the incumbent himself tallied 720,000 personal votes, also far and away the most.

During a visit to Doha as part of a tour of Gulf Arab countries, Philip Hammond, the UK's defence secretary, told Al Jazeera: "What we need to see is the leaders of all of the communities speaking out for the future of a unified Iraqi state.

"There needs to be a step change, a change of tempo, and a really significant signal to the Sunni community and Kurdish community that the government wants to change course and become a government of all of Iraq."

Referring to the main Sunni rebel group the Islamic State of Iraq and the Levant, Hammond said: "If ISIL gains control of a space in Syria or Iraq, it will use that position as a platform to launch attacks on the Gulf Cooperation Council countries. [ISIL] will be a source of instability in the region and beyond."

In Wednesday's other Iraq-related developments, Iraqi state TV broadcast video claiming to show Iraqi troops in control of the oil refinery at Baiji, amid contesting claims as to who was in control there.

The footage, shot by a journalist sympathetic to the government, shows an army helicoper briefly landing at the site before leaving.

Our correspondent reported that the video, which the government said was shot on Tuesday, seemed to suggest Iraqi troops were in control of at least part of the refinery.

The Iraqi government would have been hesitant to send a journalist to the area if it was not confident it was clear of rebels, he said.