BEIRUT — Two major links with the outside world were shut down in Syria on Thursday when Internet access disappeared across the country — raising fears of an impending escalation of the government’s crackdown on the uprising there — and the largest commercial airport in the capital was shut down because of fighting nearby, opponents of the Syrian government said.

Two companies that monitor Internet traffic, Arbor Inc. and Cambridge-based Akamai, released data suggesting that the outage had continued for several hours since about 10 a.m. Syrian time, and that there was no indication it had stopped.