Stocks were likely to face selling pressure at the start of trading Monday as North Korea took a step forward in its nuclear ambitions, making for a nervous market to open the week.

Futures on the

S&P 500

were down 2.3 points at 1356.50, about 1 point below fair value. Nasdaq 100 futures were falling 3 points to 1697 and were 2.7 points under fair value.

Lending to the early unease was a claim out of North Korea that it had successfully detonated a nuclear weapon in an underground test. Both South Korea and China denounced the North Korean leadership following the test.

Stocks fell in South Korea and Hong Kong after the report, but indices in mainland China moved higher. Tokyo's markets were closed for a holiday.

Back in the U.S., the major averages appeared to be set to continue Friday's weakness, when a weaker-than-expected jobs report and a selloff at

General Motors

(GM) - Get Report

led to a lower finish.

The

Dow Jones Industrial Average

, which had closed at record highs for three straight days, lost 16.48 points, or 0.14%, to 11,850.21, and the S&P 500 slipped 3.64 points, or 0.27%, to 1,349.58. The

Nasdaq Composite

shed 6.35 points, or 0.28%, to end at 2,299.99.

Dominating the corporate news were mergers and acquisitions. The biggest confirmed deal involved a plan by

PNC Financial

(PNC) - Get Report

to pay $6 billion for Baltimore's

Mercantile Bankshares

(MRBK) - Get Report

. Pittsburgh-based PNC will pay $47.24 a share for Mercantile.

Rumors of other takeovers were also making the rounds, including one in the tech space, where reports say

Google

(GOOG) - Get Report

is considering laying out $1.6 billion for the popular online video site YouTube.

Elsewhere, the Dolan family is aiming to buy out the public stockholders of the company it controls,

Cablevision Systems

(CVC)

. A report in

The Wall Street Journal

said the Dolans offer would value the company $7.9 billion and cited people who had knowledge of the matter.