London - Talks to resolve Northern Ireland's political stalemate reached the "end of the road" on Sunday, the Sinn Fein party said, but London still hopes to end the deadlock ahead of a Monday deadline.After three weeks of talks to form a power-sharing executive in the province - a cornerstone of peace in Northern Ireland - Sinn Fein said no deal had been reached.Sinn Fein, representing Catholic Irish nationalists, and the Democratic Unionist Party (DUP) of the pro-British Protestants, have until Monday afternoon to reach an agreement or control could return to London."Today we have come to the end of the road," said Michelle O'Neill, the party's leader in Northern Ireland."The talks process has run its course and Sinn Fein will not be nominating for the position of speaker or for the executive office tomorrow."The political crisis began when O'Neill's predecessor, Martin McGuinness, stepped down in protest at the handling of a botched green energy programme by the DUP leader and First Minister Arlene Foster.McGuinness died on Tuesday of a rare heart condition.Despite Sinn Fein's assertion that talks were over, the British government said it was still determined to see a "functioning executive" put in place."Even at this stage I urge political parties to agree to work to form an Executive and provide people here with the strong and stable devolved government that they want," said James Brokenshire, the UK's Northern Ireland minister, who has been chairing the Belfast talks.If Northern Ireland's main parties fail to reach a deal by the Monday deadline, Brokenshire will intervene, which could lead to direct rule from London being imposed.The minister could also call fresh elections, although those held in March following McGuinness's resignation failed to resolve the differences between Sinn Fein and the DUP. The DUP won 28 seats in the March 2 election, while Sinn Fein won 27 seats in the 90-seat assembly in the March 2 election, while the DUP took 28, with unionist parties losing their absolute majority in Northern Ireland's legislature for the first time since the creation of the province in 1921.