Updates prices, details throughout and analyst comments

April 7 (Reuters) - Canada's main stock index slipped on Tuesday as investors monitored the situation in the Middle East, after Iran showed no signs of relenting to U.S. President Donald Trump's ultimatum to reopen the Strait of Hormuz.

At 10:55 a.m. ET, the S&P/TSX Composite Index .GSPTSE was down 0.1% at 33,149.58 points.

As Trump's deadline approached, the U.S. intensified strikes on Iran, targeting Kharg Island, home to Tehran's main oil export terminal.

Trump has given Iran until 8 p.m. ET - 3:30 a.m. in Tehran - to end its blockade of Gulf oil or face massive destruction of its infrastructure.

"If the U.S. were to go into Iran and do what they say they're going to do, the markets will probably react negatively initially, but then they will likely respond positively thinking this is closer to an end," said Allan Small, senior investment advisor at Allan Small Financial Group with iA Private Wealth.

"Being in this state is not good for the markets, we are in limbo".

Escalating Middle East tensions pushed eight of the ten major sectors on the TSX into negative territory, with energy and utilities among the only sectors in green as oil prices extended gains.

U.S. West Texas Intermediate crude futures CLc1 surged above $115 a barrel, while Brent crude futures LCOc1 hovered near $110, pushing the energy subindex .SPTTEN up nearly 2%. O/R

The healthcare sector .GSPTTHC led losses on the benchmark index with a 1.8% decline, while consumer discretionary stocks .GSPTTCD slipped more than 1%.

The gold sub-index .SPTTGD and the materials sector .GSPTTMT, which includes stocks of metal miners, dropped 0.4% as silver fell 3%.

Meanwhile, heavyweight financials .SPTTFS were down 0.1%.

On the economic front, data showed Canadian economic activity contracted in March for the first time in four months as inflation pressures increased.

Among individual stocks, International Petroleum IPCO.TO climbed 5.2% after BMO Capital Markets upgraded it to "outperform" from "market perform".