The Bonn government on Saturday rejected charges that it had covered up the involvement of West German firms in a Libyan chemical plant that Washington says will produce nerve gas.

Chancellor Helmut Kohl's spokesman said an early release of West German intelligence reports would have endangered official probes into the affair.Spokesman Friedhelm Ost said the government had known of suspicions against the firms since October. Kohl had earlier said the first warning had come from Secretary of State George Shultz in November.

Libya says the plant at Rabta will produce only medicines.

Opposition parties, however, attacked Kohl on Saturday for his "cover-up attempts" and evasive statements.

"Against this background, his behavior in this matter is downright outrageous," Social Democratic Party leader Hans-Jochen Vogel said.

Even Kohl's Free Democratic Party allies have demanded a parliamentary investigation into the government's behavior.

Kohl's spokesman said West German intelligence had reported on poison gas projects in the Middle and Near East since the early 1980s.

"From the very beginning the government took very seriously every indication of possible, even indirect, participation by (West) German firms in the chemical factory in Libya," Ost said.

So far, investigators had been unable to find evidence to stand up in court, he said, although he said the seizure of 12 boxes of documents from the Frankfurt firm Ihsan Barbouti International had merely strengthened suspicions.