Tensions over Iraq resurfaced in the United Nations Security Council last night when the United States pressed for agreement that the chief weapons inspector, Hans Blix, should ignore an old timetable for disarming the country that could slow down Washington's plans for war.

Arguments over the pace of the inspections broke out even as news came from Baghdad that inspectors had found 11 empty chemical warheads.

At issue is the status of the resolution that was adopted by the Security Council in December 1999, which created the inspections regime headed by Mr Blix in the first place. That text, Resolution 1284, set down a calendar for inspections that could last at least a year.

On Tuesday, Condoleezza Rice, the US National Security Adviser, discreetly visited Mr Blix in New York to urge him to lay aside the timelines of 1284 and take guidance solely from the much more recent Resolution 1441, which was passed last November, giving Iraq one last chance to fall into line or face "serious consequences".

That would require the 15-member Security Council to declare Iraq in "material breach" of its disarmament obligations.

Tony Blair's Cabinet agreed yesterday to press the Bush administration to support plans to secure a new UN resolution to authorise military action – partly in an attempt to quell the revolt inside the Labour Party. But the signals from Washington were less sympathetic to a further round of negotiations at the UN, which could delay a war in Iraq.

Diplomats admitted it was highly unlikely that other Security Council members would acquiesce to the US, widely perceived as moving too fast towards war and giving too little time for the inspections to work. A British government source said: "We do not regard January 27 as a deadline. We want the inspectors to have the time and space to finish their work."

Mr Blix is legally obliged at the moment to set his compass by both of the texts concurrently. That will only change if the Security Council agrees on yet another text, in effect voiding the timelines set down in Resolution 1284 – but this is a step a majority of the Council will resist.

Part of the split in the Security Council is about the importance of 27 January, the date when Mr Blix will present the 15 ambassadors with his first substantive report on how the resumed weapons inspections are going.

Washington is increasingly indicating that it considers that day to be the point from which war preparations should go into high gear. By contrast, other countries are playing down the significance of Mr Blix's first report.

Mr Blix intends to respect the parallel calendar for inspections and his cycle of reports as laid down in the earlier Resolution 1284. This will entail him coming back to the Security Council at the end of March with a separate report detailing what disarmament tasks Iraq will have to complete in the months following.

America is fearful that this new date at the end of March will inevitably slow the momentum towards any agreement to authorise force. And America's military planners can't wait that long. By the start of April, the desert cauldron will already be heating up.